Aim: To investigate the clinical characteristics of patients with Peyronie's disease (PD) and diabetes mellitus (DM). Methods: During an 8-year period, a total of 307 men seen at our outpatient clinic were diagnosed with PD. Clinical characteristics, penile deformities and the erectile status of patients with PD and DM together (n = 102) were retrospectively analyzed and compared to patients with PD alone with no risk factors for systemic vascular diseases (n = 97). Results: The prevalence of PD among men with DM and sexual dysfunction was 10.7%. The mean age of diabetic patients with PD was (55.9 +/- 8.9) years; in the no risk factor group it was (48.5 +/- 9.0) years (P < 0.05). The median duration of DM was 5 years. The majority of diabetic patients with PD (56.0%) presented in the chronic phase (P < 0.05), and they were more likely to have a severe penile deformity (> 60 degrees) than the no risk factor group (P < 0.05). In the diabetic group, the most common presenting symptom was penile curvature (81.4%), followed by a palpable nodule on the shaft of the penis (22.5%) and penile pain with erection (14.7%). A total of 19.6% of patients were not aware of their penile deformities in the diabetic group. Erectile function, provided by history and in response to intracavernosal injection and a stimulation test, was significantly diminished in patients with PD and DM (P < 0.05). Conclusion: DM probably exaggerates the fibrotic process in PD. Diabetic patients with PD have a higher risk of severe deformity and erectile dysfunction (ED). PD seems to be a silent consequence of DM and should be actively sought in diabetic men.