The metastatic cascade depends on the presence of tumor cells which are capable of proliferation as well as of invasion with active motility. In the present study, it was examined whether the demonstration of both features in the primary lesion of malignant melanoma of the skin carries prognostic significance. Proliferation was assessed by mitotic counts and Ki 67 staining, and motility was estimated by image analysis and comparison of the image analysis results with computer simulations; 27 cases of primary malignant melanoma with a maximum vertical tumor thickness exceeding 1 mm were prospectively sampled. Mitotic counts were carried out on H & E stained sections, image analysis of the tumor pattern on S-100 immunostained paraffin slides, and Ki 67 labeling of actively cycling cells was evaluated on frozen sections. Neither proliferation nor pattern analysis alone provided a significant prognostic result with respect to overall survival and to metastasis free survival. The estimates of motility, derived from a combination of pattern analysis and proliferation values, however, proved to be significant predictors of overall survival and metastasis-free survival (log rank test: p less than or equal to 0.05). The motility features were superior to Clark level and Breslow index in this set of cases. The results demonstrate that the assessment of tumor cell proliferation and motility in histological sections may reflect the metastatic potential of primary malignant melanomas of the skin.