A 48-year-old Japanese woman with adult T-cell leukemia/lymphoma (ATLL), histologically presenting CD30-positive large cell lymphoma is reported. The patient, who was from an ATLL endemic area in Japan, had cutaneous nodules in the head, trunk, and extremities, and cervical lymph node swelling; these had been found three months before her admission to our hospital. A biopsy specimen of a skin lesion showed diffuse large cell lymphoma; the lymphoma cells were positively stained with CD30 (Ki-1/Ber H-2), CD4 (helper-T), and CD25 (interleukin-2 receptor) antibodies. Anti HTLV-1 antibody (ATLA) was detected in the serum, and molecular cytogenetic studies of lymphoma cells showed both positive T-cell receptor rearrangement and HTLV-1 specific DNA sequences.