BACKGROUND: Control of hyperglycemia in diabetes mellitus through diet, exercise, oral hypoglycemics and insulin has underlined the medical treatment for that disease. Morbidly obese diabetics can be more successfully rendered euglycemic if their excess body weight is reduced and their diets are carefully controlled. METHODS: Roux-en-Y Gastric Bypass has been used as a weight control measure for 205 morbidly obese diabetics over an 8-year period, 1988-1995. Early follow-up has been possible in all patients up to 3 months, and late follow-up has been achieved by phone contact and office visits in 133 patients. RESULTS: Operative mortality occurred in 1/205 patients (0.49%). Major operative morbidity occurred in 14/205 (6.8%). While 46/133 (35%) patients were on insulin preoperatively, only 11/133 (8%) have remained on insulin and 9/11 at lower doses. 64/133 (48%) were on oral hypoglycemics, but only 8/133 (6%) continue their use. 23/133 (17%) were on diet alone or no treatment before surgery, and 91/133 (68%) claimed diet alone or no treatment after surgery. The long-term mean % Excess Body Weight Loss is 55%. CONCLUSIONS: Morbidly obese diabetics undergoing Roux-en-Y Gastric Bypass can experience markedly diminished need for insulin and oral hypoglycemics to control hyperglycemia.