Tumor vascularity has been reported to be a prognostic factor in solid tumors. We studied the prognostic value of tumor vascularity in 19 primary stage I skin melanomas. Only intermediate-thickness melanomas (0.76-4.00-mm thick) were studied. They were treated surgically to provide two groups of patients. The first group of 11 patients had no evidence of metastases after a follow-up of a mean period of 72.36 months, whereas the second one developed metastases in a mean period of 46.87 months. The two groups were matched for important prognostic factors including tumor thickness, sex, and age. Vascularity was quantified by a morphometric stereological analysis on paraffin sections stained with anti CD31 monoclonal antibody. The percentage of vascular area was significantly higher in the metastasizing group than in the nonmetastasizing one. Our study suggests that increased vascularity may have a prognostic significance in intermediate-thickness melanoma.