The subject of the relationship between congenital nevocytic nevi and malignant melanomas has many controversial aspects. Data are insufficient to come to firm conclusions concerning how often melanomas supervene in such nevi and to determine the prognosis of those melanomas. What data are available indicate that malignant melanomas develop in a substantial percentage of large (giant) nevocytic nevi. This lends support to those who recommend surgical excision of such large lesions, when feasible. On the other hand, the information currently available concerning the association of malignant melanomas with medium- and small-sized congenital nevocytic nevi (i.e., those less than 20 cm in largest diameter) is scanty. Because of this lack of data on congenital nevocytic nevi, our current approach is to take into consideration the probability of cosmetic improvement by surgical removal in conjunction with education of the patient and/or family that malignant melanomas have been known to occur in congenital nevocytic nevi but are probably rare except in nevi of large size. Such information provided to the patient and/or family will often help in making the decision for removal or continued observation. A Congenital Nevocytic Nevus Registry has been established in the Oncology Section of the Skin and Cancer Unit at New York University Medical Center in the attempt to begin a long-term prospective study which might eventually provide some meaningful information concerning the natural history of such lesions, including the incidence of malignant melanomas.