• Working together
    to deliver the best healthcare.

Peninsula Gastrointestinal Specialists welcomes you!

Gastroenterologists in San Mateo, CA and surrounding areas.

At Peninsula Gastrointestinal Specialists, we believe that each patient and doctor become a team for treating an individual's digestive problems. Our board-certified gastroenterologists spend most of their time listening to understand your concerns and responding with the best treatment options for you. With the help of our professional staff, they also follow up to make sure that problems are resolved and your health improves.

We want our patients to be informed about their digestive problems and treatments, because informed patients make better decisions about their health and well being. That is why we've included a section on this website covering common topics associated with gastroenterology and endoscopic procedures. We encourage you to look through these pages whenever you have an interest or concern related to your digestive health.

We also know that convenience is important to your selection of a gastroenterologist in San Mateo. In these web pages you'll find information about Peninsula Gastrointestinal Specialists ' office, including our location, maps, directions, hours, insurance policies, and appointment scheduling. Please feel free to contact us with any questions you have or to request an appointment . We hope you find our practice offers the accessibility and personal commitment you look for from a gastroenterologist in the peninsula.

Meet Our Doctors

  • Edward K. Onuma
    MD, PhD

    Dr. Edward Onuma completed his undergraduate work at Cornell University and received his Ph.D. in physiology at SUNY at Buffalo, NY.  He received his medical degree at SUNY Health Science Center at Syracuse, NY in 1990.

    Read More
  • Eugene Y. Lee

    Dr. Lee graduated with honors from Columbia College of Columbia University after which he received his MD degree from NYU School of Medicine in 1998.  He completed internship and residency in Internal Medicine at the University of Rochester/Strong Memorial Hospital.

    Read More

The Blue Star

Proud Sponsor of:
Strides for Life

Colonoscopy Assist

Combined Stats:

Years in training:  15
Years in practice:  40
# of procedures performed:  40,000
ADENOMA detection rate:  above 45%


    Peninsula GI Specialists, are outstanding in all areas, I wish they could be my primary Dr's I have recommended them to friends and family, and will continue to praise them.

    Cindy C.

    Dr. Eugene Lee is an outstanding doctor!  I had a colonscopy and he was very professional and accomodating.  His staff were super nice and efficient. The colonscopy center was very up to date and friendly. Dr. Lee followed up with me three times after the procedure.  I recommend Dr. Eugene Lee!

    Theresa B.

    Dr Onuma is my second opinion dr He is very kind and concerned about all your health conditions.He knows how to explain, listen and speaks to his patient. To me having others medical conditions and being treated for different specialists . The main key for a good dr is having all good !!! Mentioned above !!! That I was missing from my previous Gastrentologist . Excellent and I will recommend him 100%.


    Dr Lee office usually don't have to wait more than 15 minutes, he is a real good surgeon when I do the surgery I don't feel nothing do a real good job.

    William W.

    Dr. Onuma is a fantastic doctor! He takes the time to listen to you and your concerns. He also takes the time to get to know you. He is great at returning calls if you have a concern or need anything. I am so grateful that I found him!

    Verified Patient

    Great experience with doc and staff.  The colonoscopy was a breeze too!

    Caroline L.

    Dr. Lee is wonderful.  He saved my Father's life -- he knew what was going on and was able to solve my Fathers problem.  As everybody mentioned in their review, he was very nice, soft spoken and knowledgeable.

    Jackie J.

Our Location

Find us on the map

Office Hours

Our Regular Schedule


9:00 am-12:00 pm

2:00 pm-5:00 pm


9:00 am-12:00 pm

2:00 pm-5:00 pm


9:00 am-12:00 pm

2:00 pm-5:00 pm


9:00 am-12:00 pm

2:00 pm-5:00 pm


9:00 am-12:00 pm

2:00 pm-5:00 pm