The lung is a preferential site for human T-cell lymphotropic virus type I infection. This peculiar tropism for the lung is responsible for the high incidence of pulmonary involvement in patients with human T-cell lymphotropic virus type I infection. A variety of pulmonary manifestations may be present in human T-cell lymphotropic virus type I-associated pulmonary diseases, but the characteristic features of this disorder appear to be chronic bronchioloalveolitis with or without fibrotic changes of surrounding parenchyma. As for the pathogenesis of pulmonary involvement associated with human T-cell lymphotropic virus type I infection, immunologic mechanisms through T-cell activation may play an important role. Such attractive interpretations need further verification.