Bone scintigraphy in 26 patients with adult T-cell leukemia-lymphoma (ATLL) was evaluated. Abnormally high accumulations were observed in 7 of 26 patients (skull, 5; vertebra, 1; rib, 6; bony pelvis, 1; scapula, 2; lower extremities, 1). Serum calcium levels were significantly elevated in patients with abnormally high accumulations on bone scintigraphy. Survival rates of the patients with positive results on bone scintigraphy were significantly lower than were those with negative results on bone scintigraphy (P < 0.05). Survival rates of patients with high serum calcium levels, high WBC counts, and high serum lactate dehydrogenase (LDH) levels were also significantly lower than were those of the negative groups, in this order of significance. Bone scintigraphy was useful for detecting bone marrow involvement in ATLL and it can be one of the better indicators of the prognoses of patients with ATLL.