A 25-year-old woman presented with an eroded mamillated plaque on her right thigh that was present since birth and had grown proportionately with age. She denied pain or pruritus, but it was frequently traumatized and occasionally became more swollen and irritated with menstruation. The patient was otherwise healthy and medical history was noncontributory. There was no family history of similar lesions. Physical examination revealed a discrete V-shaped area on the right anterior thigh composed of 0.5-cm to 4.0-cm grouped erythematous, firm papules and nodules, some with overlying serum and crust (Figure 1). A punch biopsy was performed (Figure 2 and Figure 3).