A 53-year-old woman from the Pacific region of Colombia presented with a 6-month history of pruritic papules that coalesced to form plaques in the extremities (panel A). She denied weight loss, fever, or diaphoresis. No palpable lymphadenopathy or hepatosplenomegaly was present. Laboratory examination revealed an elevated lymphocyte count of 6.2 × 10 9/L (reference range, 1.0-3.0 × 10 9/L). Calcium level was normal, whereas lactate dehydrogenase was slightly increased. Lymphocytes with flower-shaped nuclei (panel B; Wright stain, ×100) were seen in the peripheral blood smear. The immunophenotype of the cells was positive for CD3, CD4, and CD25 (strong), whereas it was negative for CD7. A skin biopsy exhibited infiltration by lymphoid cells that showed positive staining for CD3 and CD4, with loss of CD7 (panel C; hematoxylin and eosin stain, ×40, and immunohistochemical stain, ×40). Serological testing for human T-lymphotropic virus 1 (HTLV-1) was positive. A diagnosis of adult T-cell leukemia/lymphoma (ATLL) was made and treatment with interferon-α and zidovudine was started.ATLL is a lymphoid malignancy closely associated with the oncogenic HTLV-1. This infection is endemic on the Pacific coast of Colombia and is usually acquired during early childhood by vertical transmission. Clinical course is variable, and skin and peripheral blood involvement is common in the chronic leukemic variant.