Histopathologic spectrum of clinically atypical melanocytic nevi. II. Studies of nonfamilial melanoma [published erratum appears in Arch Dermatol 1990 Dec;126(12):1616] We studied the clinically most atypical pigmented lesion removed from each of 142 patients with newly diagnosed sporadic melanoma. The specimens were categorized as to the type of nevus, ie, junctional or compound, presence of congenital features, and degree of nuclear atypicality--presence of nuclear enlargement, nuclear pleomorphism, hyperchromatism, and prominent nucleoli--of intraepidermal nevomelanocytes. The frequency of nuclear abnormality was graded as 1 (rare cells), 2 (10% to 50% of cells), or 3 (greater than 50% of cells) for each nuclear parameter. Among all lesions, 42 (29.6%) were junctional nevi, 74 (52.1%) were compound nevi, and 14 (9.9%) were dermal nevi. Eighteen percent of the total were either dysplastic nevi (23 cases) or malignant melanoma in situ (three cases). Fourteen nevi (9.9%) had congenital features. There were 12 junctional and 39 compound nevi and one dermal nevus that exhibited nuclear abnormality, but only four junctional nevi compared with 19 compound nevi had sufficient atypia for a designation of dysplastic nevus. Only two nevi with congenital features demonstrated any nuclear abnormality, and these were clearly nondysplastic. Thus, among nevi surgically removed as the clinically most atypical lesion in this study, compound nevi were much more likely to demonstrate nuclear atypia (and dysplasia) than were other nevi, ie, junctional or dermal nevi, or nevi with congenital features. 