If you’ve been referred for a swallow study, you’ll usually hear one of two names:

• MBSS / VFSS (Modified Barium Swallow Study / Videofluoroscopic Swallow Study)
  
• FEES (Flexible Endoscopic Evaluation of Swallowing)

Both are instrumental swallowing assessments used to evaluate dysphagia, aspiration risk, and why swallowing is breaking down. The difference is how they “see” the swallow and what clinical questions they answer best.

ASHA describes VFSS (also called MBSS) as a radiographic procedure providing a dynamic view of oral, pharyngeal, and upper esophageal function.
ASHA describes FEES as a portable procedure using a transnasal endoscope that can be completed at bedside or outpatient clinic space.

Quick Take

• MBSS/VFSS is an X-ray video swallow study that shows bolus movement from mouth → throat → upper esophagus in real time.
  
• FEES is an endoscopic swallow study through the nose that shows throat anatomy, secretions, and residue patterns before/after swallows, often at bedside.
  
• You don’t “choose” randomly: the right test depends on the question: timing/airway invasion/UES opening (often MBSS) vs secretions/residue/fatigue/bedside feasibility (often FEES).
  
• If aspiration risk is suspected, instrumental assessment is often needed because bedside impressions can miss aspiration (including silent aspiration).

What each test is

MBSS / VFSS (Modified Barium Swallow Study / Videofluoroscopic Swallow Study)

What it is: A moving X-ray swallow study performed in radiology. You swallow barium-coated liquids and foods while the team watches bolus flow in real time. ASHA notes VFSS/MBSS provides a direct dynamic view of oral, pharyngeal, and upper esophageal function, and is typically conducted by an SLP and radiologist.
Cleveland Clinic also describes VFSS as fluoroscopy imaging that shows what happens as food and liquid move from mouth through throat to esophagus.

FEES (Flexible Endoscopic Evaluation of Swallowing)

What it is: A small flexible endoscope is passed through the nose to view the throat and larynx. ASHA describes FEES as portable and often performed in clinic space or at bedside, with an endoscope passed transnasally.
Johns Hopkins similarly describes FEES as an assessment in which an SLP passes a thin flexible instrument through the nose to assess swallowing.

MBSS vs FEES: what each one shows best

MBSS/VFSS is often best for:

• Timing of swallow initiation and airway closure (before/during/after swallow patterns)
  
• Bolus flow through oral + pharyngeal + upper esophageal stages (including UES opening dynamics)
  
• Testing compensatory strategies in real time (sip size, pacing, posture) while seeing immediate effects

FEES is often best for:

• Secretions management and airway protection at rest (before swallowing)
  
• Residue patterns after swallowing (where residue sits and how much remains)
  
• Fatigue effects across a longer session (common in neuromuscular disease and frailty)
  
• Bedside feasibility (hospital/rehab settings) because FEES is portable

Side-by-side comparison table

How clinicians decide: the “question-first” rule

A good referral is driven by what you need to know:

Choose MBSS/VFSS when the key question is:

• When does airway invasion happen (before/during/after swallow)?
  
• Is UES opening or upper esophageal clearance part of the problem?
  
• Which compensations change bolus flow timing most effectively?
  ASHA emphasizes VFSS’s dynamic visualization of oral, pharyngeal, and upper esophageal function.
  

Choose FEES when the key question is:

• Are secretions pooling?
  
• How much residue remains, and where?
  
• Does fatigue worsen residue and airway risk over the meal?
  
• Is bedside evaluation needed (can’t travel to radiology)?
  ASHA emphasizes FEES portability and bedside feasibility.
  

Many patients benefit from both at different points—especially when the clinical question changes.

What it feels like (so patients aren’t surprised)

MBSS/VFSS experience

• You’ll be seated/standing as directed in front of the fluoroscopy unit.
  
• You swallow small amounts of barium liquids and barium-coated foods.
  
• The team may test strategies (smaller sips, posture changes) to see what improves safety/efficiency.

FEES experience

• A clinician passes a thin flexible scope through the nose.
  
• You’ll swallow colored liquids/foods while the clinician observes anatomy, secretions, and residue patterns.
  
• Many people describe it as uncomfortable but tolerable; it is typically quick once the scope is placed.

How to prepare 

For MBSS/VFSS

• Bring a list of “problem foods” and “safe foods.”
  
• Ask if you should avoid eating immediately before (instructions vary by site).
  
• Tell the team about pregnancy status and prior reactions (if relevant).

For FEES

• Arrive ready to discuss nasal sensitivity, frequent nosebleeds, or anticoagulants (the team will screen appropriateness).
  
• Bring examples of the foods/liquids that trigger symptoms if asked.

How results are reported (and what matters most)

A high-quality report should answer:

1. Is there penetration or aspiration?
2. When does it happen (before/during/after swallow)?
   
3. Why (timing, residue, UES opening, reduced sensation)?
   
4. What improves it (strategy trials)?
   
5. What is the plan (safety now + rehab + follow-up)?

If airway invasion is reported, clinicians may use the Penetration–Aspiration Scale (PAS) (Rosenbek et al.) to describe depth and whether material is cleared.

What happens after: swallowing therapy and next steps

Your SLP plan typically includes:

• Immediate safety strategies (pacing, sip size, posture changes if proven helpful)
  
• Diet/texture guidance only when necessary, with an explanation of “why” and “for how long”
  
• Rehab targets based on the physiology seen on MBSS/FEES (skill-based swallowing therapy is highly individualized)
  
• Medical coordination if esophageal issues or reflux/inflammation patterns are suspected

ASHA positions SLPs as key providers in adult dysphagia management and emphasizes the role of instrumental assessment resources (VFSS/FEES) in guiding care.

Symptom → Test Map

Where BreatheWorks fits

BreatheWorks is a speech-language pathology practice with a whole-patient approach that supports patients from infancy through geriatrics. Care may include speech/voice, feeding/swallowing, orofacial myofunctional therapy (OMT/OMD), and TMJ, with an emphasis on root-cause assessment across areas like sleep and breathing when relevant. You can start with in-person care at a clinic or choose secure virtual therapy with the same patient-centered model.

FAQ: MBSS vs FEES 

Is MBSS the same as VFSS?

MBSS is commonly used interchangeably with VFSS. ASHA notes VFSS is also known as the modified barium swallow study and is a radiographic procedure showing oral, pharyngeal, and upper esophageal function.

What does an MBSS/VFSS show?

It shows real-time X-ray images of swallowing as food/liquid moves from mouth to throat and into the upper esophagus, helping identify timing and airway invasion patterns.

What does FEES show?

FEES shows the pharynx and larynx via a transnasal endoscope and helps evaluate secretions, residue, and airway protection before/after swallowing; it can be done bedside.

Which test is better for aspiration?

Both can identify aspiration risk, but they answer different questions. MBSS is strong for timing and bolus flow (including upper esophagus), while FEES is strong for secretions/residue and fatigue patterns.

How do I know which swallow study I need?

Your clinician should choose based on your symptom pattern and the clinical question (timing/UES vs residue/secretions/bedside feasibility).

Can I do either test if I’m medically fragile?

Often yes, but setting matters. FEES can be performed bedside; MBSS requires transport to radiology. Your medical team will decide the safest approach.