BackgroundThe prepuce (foreskin) is a simple fold of skin formed from an outer keratinized layer and inner mucosallayer, lining a preputial sac and provides functions such as protective, erogenous, and immunologic. Theprepuce is normally non-retractile during neonatal development, as the inner epithelial lining of prepuceand glans adhere each other. Non retractile prepuces are common among young boys and normalpart of preputial development. However, unnecessary circumcision is widely practiced among youngadolescents due to poor understanding of foreskin and lack of medical indication.GoalTo assess preputial retractibility in Mongolian boys at various ages to determine natural process ofpreputial separation.Material and MethodsWe evaluated 1697 Mongolian boys aged 2 to 12. Preputial condition was classifi ed into 5 types basedon preputial retractability: type I-phimosis, type II–partial phimosis, type III–adhesion of prepuce, IV–normal, V–circumcised. We also prospectively evaluated 30 histological materials of patients (2-12 yearsold), who were treated by complete circumcision. The materials were fi xed 10% solution of formalin,embedded in paraffi n, stained with hematoxylin-eosin and examined by 3 pathologists.ResultsThe incidences of type I was 67.9% in 2 years old, 12% in 6years, and 4.1% in 10 years and1.1% in12 years old, respectively. On the contrary, the incidences of type IV were 15.4% in 2 years old, 29.8%in 6 years, 74.7% in 10 years and 91.6% in 12 years. Thecircumcisionswere0% in 2 years old, 5.7%in 6 years old, 2.9% in 10 years old and 5% in 12 years old. Most patients (76.7%) did not have anyhistological alterations of the skin and infl ammatory alteration, not lichen sclerosis, were observed in23.3% in histological examination followed by circumcision.Conclusion: Preputual separation increases with ages in boys and surgical treatment of the phimosisshould be performed with cautions.