Adult T-cell leukemia/lymphoma (ATLL) has been divided into four subtypes up to now: (i) acute; (ii) lymphoma; (iii) chronic; and (iv) smoldering. Skin lesion(s) may be present and the cases showing less than 5% abnormal T-lymphocytes in peripheral blood without involvement of other organs, have been classified as smoldering ATLL. However, this type of ATLL with skin manifestations had a worse prognosis than that without skin lesions. This study aimed to define and distinguish cutaneous ATLL lacking nodal lymphoma and leukemic change from smoldering ATLL. We propose an entity of cutaneous ATLL, which has less than 5% abnormal T lymphocyte in peripheral blood, a normal lymphocyte count (i.e. <4 × 109/L), no hypercalcemia and lactate dehydrogenase values of up to 1.5 times the normal upper limit. At least one of the histologically proven skin lesions should be present accompanying monoclonal integration of human T-cell lymphotropic virus type 1 (HTLV-1) proviral DNA in the skin lesion. Blood samples were collected from 41 HTLV-1-infected patients, 21 asymptomatic carriers, 16 patients with cutaneous ATLL and four patients with smoldering ATLL. HTLV-1 proviral loads, soluble interleukin-2 receptors and other parameters were examined in each case. HTLV-1 proviral DNA loads in smoldering ATLL group are significantly higher than those in asymptomatic carrier and cutaneous ATLL group. Cutaneous ATLL may be a distinct entity that should be separated from smoldering ATLL clinically and virologically.