A 58-year-old white man had dermatomyositis and primary cutaneous B-cell lymphoma. The cutaneous lymphoma was evidenced by a noduloulcerative disease of the lower extremities. Histologic results resembled a T-cell process with a diffuse, superficial infiltrate composed of small- and medium-sized lymphocytes with angioinvasion and epidermotropism. The infiltrate extended into the deep dermis and panniculus with scattered large lymphocytes and necrosis. With the help of gene-rearrangement analysis and immunophenotyping, the true B-cell lineage was discovered. The importance of gene-rearrangement analysis and immunophenotyping in the diagnosis of cutaneous lymphoma is emphasized.