Whole-night sleep polygraph by removing the first-night effect was recorded for 15 cases of idiopathic nocturnal enuresis and 10 cases of normal control, thereby, review was made on the relation between sleep and etiology of nocturnal enuresis as well as the appearing characteristics of rhythmic slow wave. (hereinafter referred to R.S.W.). Thus the following results were obtained. Both groups of nocturnal enuresis and normal control showed no significant difference under the same experimental conditions for the rate of encephalogramic sleep stage. Nocturnal enuresis was observed in nearly the same number of cases at any stage of sleep except Stage 1 (hereinafter referred to as S), and there were many cases in the second and third sleep cycles. At the time of occurrence of nocturnal enuresis, 6-7 Hz R.S.W. continued as long as 15-40 seconds in NREM-sleep. Also, 3-5 Hz R.S.W. was observed in REM sleep. R.S.W. was observed even in normal cases, while its incidence was high in the cases of nocturnal enuresis, and the decrease was observed with advancement of age, however, the decrease was delayed in the cases of nocturnal enuresis. R.S.W. was provoked reactively against the stimuli such as the change in the electro-encephalogramic sleep stage and body movements. On the other hand, there was an inhibitory tendency of the changes in heart rate and respiration during the appearance of R.S.W. By the above result and the resemblance between R.S.W. and DR theta, R.S.W.(ABSTRACT TRUNCATED AT 250 WORDS)