Distinct congenital, benign, probably hamartomatous, lesions of the upper dermis were noted in two children who subsequently developed malignant rhabdoid tumors. The dermal lesions, which we have named "neurovascular hamartomas" were characterized by a proliferation of capillaries in a background of bland spindle cells with possible neural features. In one child the malignant rhabdoid tumor was located in the kidney, and a synchronous primitive neuroectodermal tumor of the central nervous system was the cause of his death. The other infant had two neurovascular hamartomas, and a malignant rhabdoid tumor arose in contiguity with the deepest portion of the larger of the two hamartomas. An axillary lymph node metastasis rapidly developed in this child followed by widespread metastases and death 3 months later. Neuroectodermal differentiation was observed immunohistochemically or ultrastructurally in all rhabdoid tumors and in the tumor of the brain. This is the first report of a unique congenital benign dermal lesion that appears to be associated with malignant rhabdoid tumors in very young children. A genetic abnormality of neuroectodermal differentiation may underlie the development of these neoplasms.