There are many clinical and histologic factors that are known to be valuable in predicting survival rates for patients with cutaneous malignant melanomas. Breslow thickness is considered to be the most reliable prognostic factor; however, thickness is a unidimensional measurement. A more accurate mensuration to predict biologic behavior might be one that takes into account the three-dimensional volume of the neoplasm. In a study of 35 primary malignant melanomas, the volumes of the dermal components of the tumors were calculated. Those patients with tumor volumes of 200 mm3 or less had a 91.4% 5-year disease-free survival rate, compared with survival rate of only 16.7% for those patients whose lesions had tumor volumes exceeding 200 mm3. On multivariate analysis, tumor volume exceeded thickness as a prognostic indicator. Thus, measurement of tumor volume proved to be of greater significance than thickness in predicting the outcome for patients with malignant melanomas.