Nevus sebaceus of Jadassohn is a hamartoma that combines epidermal, follicular, sebaceous, and apocrine gland abnormalities. Classically, several types of cutaneous neoplasms have been associated with this hamartoma, with basal cell carcinoma being the most frequently described malignancy. We studied a series of 155 examples of nevus sebaceus of Jadassohn with clinicopathologic correlation. Several histopathologic changes related to the age of the patients were found. In our series, we could not identify any cases of authentic basal cell carcinoma. In contrast, several examples of primitive follicular induction and of trichoblastomas were seen. Other cutaneous hamartomas, hyperplasias, and neoplasms found in our series of nevus sebaceus of Jadassohn included syringocystadenoma papilliferum, sebomatricoma, apocrine gland cyst, poroma, different histopathologic variants of warts (classic warts, tricholemmoma, and desmoplastic tricholemmoma), primitive follicular induction, and ductal induction. In our series, no examples of malignant neoplasms were identified. On the basis of these findings, the classically recommended treatment for this hamartoma, which consists of early excision to prevent the development of malignancy, seems to be inappropriate.