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License & Identifications

A medical license is required for a doctor to practice medicine in a particular state. Requirements vary by state but most require, at a minimum, post-graduate training in the doctor’s specific specialty. An NPI number is a national identifier unique to an individual health care provider and is managed by the Center for Medicare & Medicaid Services (CMS).

Learn more about Dr. Dennis O'Brien:

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  1. Qualifications
  2. What's important to you

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Patient Reviews

Patient comments (4)

The overall average patient rating of Dr. Dennis O'Brien is Good. Dr. O'Brien has been reviewed by 28 patients who have provided 4 comments. The rating is 3.5 out of 5 stars.

Patient Ratings
Ease of Appointment 3.9
Promptness 3.7
Courteous Staff 3.1
Accurate Diagnosis 3.7
Bedside Manner 3.7
Spends Time with Me 3.7
Follows Up After Visit 3.7

Specialties & Research

Dr. Dennis O'Brien, MD is board certified in Internal Medicine.

Education & Awards

Dr. O'Brien graduated from Universite De Bordeaux Ii.


Dr. O'Brien has 1 hospital affiliations:

  • St Catherine Of Siena Medical Center 


  • French

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Additional Information
Dr. Dennis Sean O'Brien MD is a male Internist, has 31 years of experience and practices in Internal Medicine.
Where does Dr. Dennis S. O'Brien practice?
Dr. Dennis O'Brien has 4 office locations.
Dr. Dennis O'Brien practices Internal Medicine near Saint James, NY.
Additional practice locations include: Smithtown, NY.
See Saint James Internists.