Certain histologic and clinical features of malignant melanoma have been shown to be indicators of prognosis, both collectively and individually. Even though the predictive value of these features is well established, long-term survival is occasionally seen in individuals with multiple poor prognostic factors. To further examine this phenomenon, histologic sections from 53 patients with malignant melanoma excised between the years 1977 and 1980 in whom reliable clinical follow-up data were obtained were evaluated for the presence of features associated with a poor prognosis (thickness greater than 1.7 mm, Clark level greater than or equal to III, vertical growth phase, high mitotic index, marked cytologic atypia, minimal tumor inflammatory infiltrate, presence of regression, presence of plasma cells, male sex, age greater than or equal to 45 years, and axial anatomic location). Sixty-eight percent of the patients survived for greater than or equal to 10 years. Of these, 26% had lesions greater than or equal to 1.7 thick. Multivariate discriminant analysis of all features provide a model that was 76% accurate in predicting outcome over a 10-year period. Although the predictive value of these prognostic variables is generally reliable, there is a significant population of long-term survivors in whom prognosis could not be accurately predicted using these features.