Human T cell lymphotropic virus type I (HTLV-I)-induced immunosuppression has been suggested to explain the occurrence of crusted scabies in HTLV-I-infected patients. HTLV-I is the etiologic agent of adult T cell leukemia/lymphoma (ATL). Crusted scabies diagnosed in 6 HTLV-I-seropositive patients was studied to look for an association with ATL. Four of the 6 either had concomitant ATL when crusted scabies was diagnosed or developed ATL a few months later. These findings suggest that the occurrence of crusted scabies in patients seropositive for HTLV-I could represent a sign of marked immunosuppression related to ATL.