A 64-year-old man presented with a two-year history of a slowly enlarging nontender pruritic mass on his left thigh. Two years prior to evaluation he had noticed two small scaling psoriasiform patches on his inner left thigh, each approximately one half inch in diameter. Treatment with topical steroid therapy for psoriasis had no effect on these lesions, whereas other psoriatic lesions on the left middle aspect of his abdomen resolved with therapy. No biopsy specimen was taken from these lesions. Over the following year the two left thigh patches expanded and coalesced, Figure 1.Figure 2.Figure 3.Figure 4.forming an elevated ringlike tumor. This tumor quadrupled in size during the next year. The patient denied any pain or weight loss. He noted a small psoriasiform lesion on his left calf at the time of admission.Physical examination revealed an annular, fungating, violaceous, weeping tumor with several ulcerations, approximately 16 X 25 cm, on the left medial and posterior aspects of the thigh (Fig 1). A second tumor of identical appear¬ ance, approximately 4.5 X 7 cm, was on the medial aspect of the left popliteal fossa. Enlarged inguinal lymph nodes were palpated bilaterally. Bone scan, left hip and left leg roentgenograms, and computed tomographic (CT) scan of the left leg revealed no muscle or bone involvement by tumor. Chest roentgenogram and CT scan of the abdomen were normal, as were the results of the following studies: complete blood cell count, serum SMA-18 chemistry analy¬ sis, quantitative immunoglobulin studies, urinalysis, bone marrow biopsy, and Sézary cell preparation. A left inguinal node biopsy specimen showed dermatopathic lymphadeni¬ tis with marked plasmacytosis. Immunologie typing and immunoperoxidase studies of a skin biopsy specimen from the larger tumor demonstrated a polytypic population of lymphocytes, predominantly T helper cells. The tumor biopsy specimen is shown in Figs 2 through 4.