Dr. Callahan is originally from York, Pa., and attended Ursinus College, graduating in 1983 with a B.S. in biology. Upon graduating, he was commissioned a lieutenant in the United States Marine Corps and served on active duty from 1983 to 1986. After receiving his degree from the Philadelphia College of Osteopathic Medicine in 1991, he served a rotating internship at Suburban General Hospital in Norristown, Pennsylvania. In 1995 he completed his internal medicine residency at the Lankenau Hospital, followed by a two-year gastroenterology fellowship at the same institution.
Dr. Callahan is board certified by the American Board of Internal Medicine in both Internal Medicine and Gastroenterology. He is a member of the American College of Physicians, the American College of Gastroenterology, the American Gastroenterologic Association, and the American Society for Gastrointestinal Endoscopy.
Dr. Callahan practiced in Lewes, Delaware prior to joining Main Line Endoscopy Center. He is married and has two sons.