This prospective study was designed to address the incidence and clinical and histologic characteristics of balanitis xerotica obliterans in a large random pediatric population with phimosis. We investigated 1178 boys who presented consecutively with phimosis between 1991 and 2001. All patients who underwent complete circumcision and surgical specimens were typed histologically as early, intermediate, or late forms of this disorder or as nonspecific chronic inflammation. Patients with balanitis xerotica obliterans were controlled at 1, 6, and 12 months postoperatively, then yearly. Balanitis xerotica obliterans was found in 471 of the 1178 patients (40%), with the highest incidence in boys aged 9 to 11 years (76%). Secondary phimosis occurred in 93% of boys with balanitis xerotica obliterans and in 32% of those without the disorder. In six instances of balanitis xerotica obliterans, meatotomy and in one meatoplasty was performed, as well as circumcision. On histologic evaluation, we found 19% had early, 60% intermediate, and 21% late form of balanitis xerotica obliterans. Glanular lesions disappeared completely within 6 months in 229 out of 231 patients. Our data strongly suggest that the true incidence of childhood balanitis xerotica obliterans is higher than previously assumed. Its incidence peaks in the 9 to 11 years age group, in whom secondary phimosis was almost exclusively caused by balanitis xerotica obliterans.