We report the rare occurrence of a trichoepithelioma within a congenital melanocytic nevus in an adult, whose clinical presentation was suspicious for malignant transformation. Dermoscopy was not reassuring, and different from previously described cases of trichoepithelioma. The occurrence on the back of a male was another peculiar finding, as usually TE arises on the face of young women. Histopathology was characteristic, with the exophytic desmoplastic trichoepithelioma surrounded by the melanocytic proliferation, and supported the hypothesis that trichoepithelioma is an acquired condition, probably induced by the release of growth factors and cytokines from melanocytes. We speculate that intense sun exposure, due to the patient’s outdoor working and sporting activities, might have activated the melanocytes, and triggered this very unusual benign proliferation. Trichoepithelioma should be included among the diagnostic pitfalls mimicking malignant proliferation inside a congenital melanocytic nevus.
