We have experienced a case of bipolor I disorder complicated by mental retardation and autistic disorder. Acquired daily life activities such as eating, clothing and toileting without assistance were gradually lost during depressive periods, which was consistent with the previous reports. Before losing daily life skills, the patient could no longer perform daily life activities without consecutive instructions. This "waiting-for-instruction" behavior may be an early diagnostic key for major depressive episode in mentally-retarded children and adolescents.