Nocturnal enuresis is the second most common chronic health problem in children following allergy. The prevalence of nocturnal enuresis in different age groups is about the same in all parts of the world. It can be stated that nocturnal enuresis is a clinical problem for the child and the family as well when the child is wetting the bed at least one night every month. With this definition, about 10% of 7-year-old children have nocturnal enuresis. Historically, a remarkable progress has been made in the mid-eighties. Previously, bedwetting was looked upon as a trivial condition, hardly worthy of serious medical assessment and management. In 1985, however, a study from Aarhus in Denmark drew a strong attention to bedwetting in the medical community worldwide by suggesting that nocturnal enuresis may be caused by nocturnal polyuria, which in turn depends on an insufficient production of antidiuretic hormone (vasopressin) during the sleeping hours. Since then, nocturnal enuresis has turned out to be an unexpectedly fruitful area for research, producing hundreds of scientific reports. Regarding its pathophysiology, it is becoming clear that two thirds of children with nocturnal enuresis have nocturnal polyuria due to an inadequate vasopressin secretion during sleep. In addition, ongoing studies suggest that there may be bladder problems (unstable bladder) or arousal disorder underlying nocturnal enuresis. Nocturnal enuresis should be taken seriously by physicians and needs intervention when the child expresses a desire to sleep dry, usually around 5 years of age.