Not only physical and mental conditions but also social adaptation of a great number of persons are often disturbed by sleep disorders. For example, unexpected inattention and drowsiness due to different sleep disorders including sleep apnea syndrome, narcolepsy, nocturnal insomnia etc, during car-driving and other working situations may lead to traffic accidents and other disasters. This indicates that sleep disorders are not only important medical but also social problems. Recent progresses in the field of sleep disorders medicine have enabled to distinguish many sleep disorders with different clinical manifestations, pathophysiologies and etiologies. Two kinds of international diagnostic classification of sleep disorders are available at present: ICSD (1990) and ICD-10 (1992). Outlines of these international classifications were introduced and their outstanding points and shortcomings were discussed.