Who is gateway medical associates? Gateway Medical Associates is a group practice with 9 locations. Currently, Gateway Medical Associates specializes in Adolescent Medicine, Diabetes, Endocrinology, Diabetes & Metabolism, Family Medicine, Geriatric Medicine, General Practice, Infectious Disease and Internal Medicine with 44 physicians.Are new patients welcome at gateway? New patients are always welcome. Gateway Medical Center was founded in 2001 by Dr. Sisom Osia. Dr. Sisom Osia graduated from the Semmelweis Orvostudomanyi Egyetem, Budapest, Hungary in 1979. He completed his residency at Howard University Medical School in Washington, D.C.How do i contact gateway health medicare advantage? General Contact Information. If you are an Agent interested in selling Gateway Health Medicare Advantage products, please call Gateway Health Agent Support at 1-888-871-0417.What are gateway medical centers hours of operation? Gateway Medical Center is open from Monday through Friday, 9:00 AM to 5:00 PM. Dr. Osia is also available by appointment for Skype meetings and consultations outside of his office hours. The office is closed on Federal Holidays. Contact Us!