Primary adrenal lymphoma (PAL) is very rare; the majority of cases reported previously were of B-cell origin. We report a rare case of primary adrenal adult T-cell leukemia/lymphoma (primary adrenal ATLL). ATLL is a highly aggressive T-cell type non-Hodgkin's lymphoma and etiologically associated with human T-cell lymphotropic virus 1 (HTLV-1). Most ATLL patients present with leukemia and widespread lymphadenopathy. A 37-year-old Japanese woman presented with back pain in January 2004. Examination showed no peripheral lymphadenopathy, circulating lymphoma cells, hepatosplenomegaly, and skin lesions. Imaging studies demonstrated large adrenal masses bilaterally. Subsequently, she underwent open adrenal biopsy and pathological diagnosis was confirmed as T-cell lymphoma. The serum antibody to HTLV-1 was positive. Southern blot analysis detected monoclonal integration of proviral DNA of HTLV-1 into host genome in the biopsy specimen. The diagnosis of ATLL arising in adrenal glands was established. Despite repeated systemic chemotherapy, the patient died of progressive disease in December 2004. ATLL could primarily involve the adrenal gland and this disease entity should be included in the differential diagnosis of adrenal mass lesions.