In this study, cytomegalovirus (CMV) infection was found in eleven of 21 autopsied cases (52.4%) with adult T-cell leukemia (ATL). Seven cases (63.6%) revealed disseminated infection in more than three organs. The lungs were involved in all eleven cases (100%), adrenal glands in eight cases (72.7%), esophagus in four cases (36.4%), and stomach, small intestine and urinary bladder in three cases (27.3%). Histopathological findings suggested that lung involvement was the cause of death in five of the 11 cases, the small intestine were involved in two of the 3 cases, and the adrenal glands were involved in one of the 8 cases. In summary, CMV infection was found to be the main cause of death in five (45.5%) of the 11 ATL patients.