Factors affecting patient compliance with diet and medication, clinical control, complications, and handicap were studied in 114 subjects with non-insulin-dependent diabetes mellitus who were attending a hospital diabetic clinic. Compliance with diet and hypoglycemic medication was correlated. The perceived importance, and the ease of compliance were the principal correlates of patient compliance. Factors independently related to diabetic control were compliance with diet, and the quality of the patient's diet. Diabetes which was poorly controlled, and which was of several-years' standing, was more likely to involve complications. Both poor control and the presence of complications contributed to handicap. Increased dietary education and counselling, with emphasis placed on the importance and benefits of compliance with prescribed diets, may improve control, decrease the incidence of complications, and ultimately minimise handicap due to diabetes in non-insulin-dependent patients.