The right gastroenterology expertise—when and where you need it.

Regional Gi formed when both of Lancaster County’s long-trusted gastroenterology practices merged. Combined, our team can now match patients with experts in virtually any digestive condition that could affect you and your family. We also have specialists in procedures such as colonoscopy, endoscopy, and advanced surgeries. You can see any clinician you choose at any Regional Gi location. Follow the links on this page to get to know our providers and review their backgrounds and clinical interests.

Photo of Mark H. Johnston MD, FACP, FACG, AGAF

Mark H. Johnston MD, FACP, FACG, AGAF

Areas of Interest
GERD, Barrett's Esophagus, Esophageal Cancer

Board Certification
Internal Medicine and Gastroenterology

Biographical Info

Board certified in Internal Medicine and Gastroenterology, Dr. Johnston is former Chief of Gastroenterology at the National Naval Medical Center and retired as a Navy Captain (0-6) in 2005.  He is the author of numerous publications, and has spoken nationally and internationally in his areas of research: GERD, Barrett’s esophagus and esophageal cancer. He is internationally known for his expertise in esophageal disease and has several U.S. Patents for the treatment of Barrett’s esophagus and esophageal cancer.  He has treated numerous members of Congress, the Supreme Court and White House.