Lichen planus is a rare disorder in infants and children where it usually has the classical cutaneous pattern and only exceptionally involves the mucosa and skin appendages. A 9-year-old boy was referred to our department with a 4-month history of erythematous keratotic papules on the trunk and the upper and lower limbs. There were no signs of mucosal involvement. Subsequently white papules and striae, occasionally forming a lace like pattern, appeared on the penis and prepuce which quickly led to phimosis necessitating circumcision. Histologic examination of skin biopsy specimens and genital mucosa fragments confirmed the clinical diagnosis of lichen planus.