Becker nevus syndrome is characterized by the presence of a particular type of organoid epithelial nevus showing hyperpigmentation, increased hairiness and hamartomatous augmentation of smooth muscle fibers, in association with other developmental defects such as ipsilateral hypoplasia of breast and skeletal anomalies including scoliosis, spina bifida occulta, or ipsilateral hypoplasia of a limb. Usually, but not invariably, all of these anomalies involve the same side of the body as the nevus. Because the nevus is androgen-dependent anomaly, the "full-blown" picture of Becker nevus is in general observed exclusively in adolescent or adult men. In women and prepubertal boys the lesion is much less conspicuous because the pigmentation is less intense and hairiness is absent or only mild. The male to female ratio of cases of Becker nevus syndrome so far reported is approximately 1:2. This is explained by the fact that unilateral hypoplasia of breast is an easily recognizable anomaly; therefore, it is more reported. Thus, it is suggested that with more thorough clinical studies the true ratio would probably be 1:1.