Dermatofibrosarcoma protuberans (DFSP) is a rare fibroblastic skin tumor of intermediate malignancy. Its pathogenesis has not yet been fully clarified. Recent basic genetic research has shown chromosomal translocations, generally termed "ring chromosomes", in DFSP. These arise from a fusion of chromosome regions 17q22 and 22q13, the gene loci which code the alpha chain of type I collagen. The diagnosis is made histologically. Differentiation from atypical dermatofibroma and dermatomyofibroma, as well as from malignant fibrous histiocytoma, whose prognosis is usually much less favorable, can be improved by immunostaining for CD 34 and Factor XIIIa. The extent of the tumors can be estimated by CT and more precisely with MRI. All these techniques fail to detect the fine tumor fascicles extending into the adjacent connective tissue and fat. Surgery is the therapy of choice for DFSP. The locally infiltrative growth pattern features clinically inapparent extensions which often extend for long distances in a horizontal direction. These tumor extensions are best detected by uninterrupted histological check of all margins, including the base (3-D-histology), with paraffin sections. Re-excision of tumor-positive areas until tumor-free margins are obtained ("histographic surgery") insures a high cure rate (97%) while preserving normal tissue.