The histological findings in the first diagnostic biopsy of 50 patients with Kaposi's sarcoma (KS) were classified and were related to the clinical course. Forty-one patients had the “classic KS,” of whom 31 had a benign course and 10 an aggressive disease. Nine patients had iatrogenically induced KS. Histologically the following subtypes were found: mixed type in 18 patients, spindle type in 16, early type in 14, and hemangiomatous and lymphangiomatous types in one each. We did not find any statistical relationship between the histological subtypes, degree of nuclear atypia, number of mitoses, and density of the inflammatory cell infiltrates in the KS lesions, and the clinical types and course of the disease. The results of this study do not support the possibility of a prognostic importance regarding the histological features of the early lesions in patients with classic or iatrogenic Kaposi's sarcoma.