Introduction: To investigate autonomic nervous system function in enuretic children by performing ambulatory blood pressure monitor (ABPM) for 24h. Methods: Twenty-eight children ranging in age from 6 to 15 years with primary nocturnal enuresis and 27 age-matched healthy controls were enrolled and they get 24h ABPM. Hypertension was defined as standard deviation score (SDS)>1.64 (i.e., >95th percentile) adjusted for gender and height. Urinalysis, urine electrolyte levels, urinary culture, and urinary system ultrasound were carried out in all children. They have also requested to have a diary about daily fluid intake and urine volume. Results: Although the mean 24-h and daytime diastolic blood pressure (BP) did not differ between the groups, systolic BP (SBP) was significantly higher in enuretic children (p<0.05). The mean night-time SBP, DBP values, SDS and BP loads were found to be significantly higher than those in the controls (p<0.01). A lack of nocturnal decrease was more prevalent in the enuretic children compared with the control subjects, the difference was statistically significant for DBP but not for SBP. Patients with elevated night-time BP load was found to have higher frequency of urinary incontinence per week as well as per night when compared with enuretic children with normal night-time BP load (r=0.72, r=0.69, p<0.01, respectively). Conclusion: Subtle abnormalities of circadian BP regulation in enuretic children indicated by a selective elevation of nocturnal SBP, DBP, and MAP, and attenuated nocturnal dipping may reflect sympathetic hyper activation and its possible role in pathogenesis of enuresis.