Objective: To clarify the pathogenesis of nocturnal enuresis. Methods: Overnight simultaneous monitoring of electroencephalogram and cystometrogram, developed in 1985, was the basic method. Results: Nocturnal enuresis was classified into types I, IIa and IIb. In type I, activation of the arousal center functioned correctly, but the development of the function to switch light sleep to complete awakening was immature. In type IIa, activation of the arousal center failed. In type IIb, transmission of the urinary sensation to the upper centrum was ineffective because of the disturbance of bladder function. Conclusion: There is a possibility that a universal concept embracing the various theories for enuresis proposed in the past could be obtained from this theory.