We prospectively investigated 100 pediatric patients suffering from phimosis and found a 10% incidence of lichen sclerosus et atrophicus. This condition usually can be diagnosed preoperatively because of its classic manifestation of severe phimosis due to a sclerotic, whitish ring at the tip of the prepuce, which in our cases was accompanied by sclerogenous glanular lesions. To our knowledge our study represents the first evidence that the development of secondary phimosis with no apparent reason in school-age boys is highly suggestive for lichen sclerosus et atrophicus. Complete circumcision is the therapy of choice because it completely removes all affected tissue and it allows spontaneous regression or resolution of glanular lesions. There has been no recurrence after 5 years of followup.