Becker nevus is a cutaneous hamartoma usually characterized by a unilateral hyperpigmentation macule associated with hypertrichosis. It is generally localized on the upper portion of the trunk, more often found in male than in female patients but usually seen only from adolescence onward. It has been suggested that Becker nevus is stimulated by androgens. Indeed, previous studies have shown that an increase in the amount of androgen receptor, as detected by ligand-binding assays, is associated with the Becker nevus of adolescent males1 as well as adolescent females.2 However, low abundant target molecules, such as androgen receptor messenger RNA (mRNA), have remained difficult to quantitate, and a correlation between the level of androgen receptor and the steady-state levels of androgen receptor mRNA expression has thus far not been explored. In the present study, we demonstrated an increase in the androgen receptor mRNA content in a Becker nevus in comparison with unaffected skin.