OBJECTIVE: The prevalence of chronic diarrhea in patients with type I and type II diabetes is uncertain, most data being available from tertiary referral centers. We report the prevalence and etiology of chronic diarrhea in 861 heterogeneous diabetic patients attending a primary care diabetic outpatient clinic. METHODS: All patients attending the clinic were asked to fill in a questionnaire relating to their bowel habits. Patients who fulfilled the criteria for chronic diarrhea underwent a comprehensive workup to define the cause of the diarrhea. Additional parameters were the mean duration of diabetes, hemoglobin-A1c levels, and the presence of autonomic neuropathy. RESULTS: Chronic diarrhea was diagnosed in 32 patients (Overall prevalence of 3.7%). The prevalence of nondiabetic diarrhea was higher among type I diabetic patients than among type II patients (3.29% vs 2.3%), although it did not reach statistical significance. Diabetic diarrhea was more common among type I than type II diabetic patients (5.2% vs 0.4%, respectively, p < 0.01). The most common cause of nondiabetic diarrhea was medication induced (metformin). CONCLUSIONS: Chronic diarrhea is more frequent in type I diabetic patients. The higher prevalence of diarrhea in this population can be attributed to diabetic diarrhea (which is quite rare in type II patients). The most common cause of nondiabetic diarrhea is drug therapy with metformin.