We report an 18-month prospective study of 90 patients undergoing penile prosthesis implantation to evaluate a possible cause-and-effect relationship between degree of diabetic control and the risk of infection complicating the operation. Long-term diabetic control was objectively evaluated by measurement of the glycosylated hemoglobin of the patient, which is known to provide an objective value for degree of control for the preceding 60 to 90 days. Of 90 patients 5 (5.5%) had a periprosthetic infection requiring explantation and all infections occurred in the 32 diabetics (36%) in the population (p less than 0.009). Of the 32 diabetics 13 (41.1%) were poorly controlled with time as demonstrated by a glycosylated hemoglobin level of greater than 11.5% and 4 of the infections occurred in this group. Of the 19 remaining controlled diabetics (glycosylated hemoglobin level less than 11.5%) only 1 infection occurred. Therefore, infection occurred in 31% of the poorly controlled versus 5% of the adequately controlled patients (p less than 0.0003). Measurement of glycosylated hemoglobin values appears to be a useful tool to evaluate diabetic patients before implantation of a penile prosthesis. Patients with a glycosylated hemoglobin level of 11.5% or greater should be more optimally controlled before undergoing implantation in an effort to avoid infectious complications.