Gastroenterologist Frederick, MD - Reflux, Stomach Pain, Ulcers - Gordon Liss. Frederick Gastroenterology Associates. We welcome you to Frederick Gastroenterology Associates. Ninth Street Medical Center. 310 West Ninth Street. Frederick, MD 21701. (301) 695-6800. Patient Portal.Our Staff‧Our Office‧Our Services‧New Patients‧Frederick Endoscopy Center‧Insurance Plans.