A classification system of enuresis was proposed based on the overnight simultaneous electroencephalographic (EEG) and cystometric (CM) monitoring of 204 cases. The classification types proposed were as follows: (a) Type I (125 cases, 61%). The first bladder contraction (FBC) in CM is noticed on cystometrogram (CMG) during Stage 4 sleep when the bladder is full. An evidence of arousals in EEG appears and EEG changes to a Stage 1 or 2 sleep pattern; however, enuresis occurs without waking. (b) Type IIa (22 cases, 11%). FBC is noticed as in Type I, but no EEG response is observed; enuresis occurs. (c) Type IIb (57 cases, 28%). An uninhibited contraction of the bladder is observed on CMG only during sleep (not on awakening). No change in either FBC or EEG is found, but enuresis occurs. It is expected that new methods of treatment for enuresis will be developed based on this classification system.