The Swedish Enuresis Trial (SWEET) was conducted to evaluate the long-term safety and efficacy of intranasal desmopressin treatment in children with primary, monosymptomatic nocturnal enuresis (PMNE). The study had an open, multicentre design and comprised a 4-wk observation period, a 6-wk dose titration period (with 20-40 microg desmopressin) and a 1-y, long-term treatment period. A treatment-free week was introduced every 3 mo to identify dry patients. In total, 399 children aged 6-12 y with PMNE were recruited. Of these, 245 patients (61%) experienced > or = 50% reduction in the number of wet nights during the last 4 wk of dose titration compared with the observation period. These responders entered the long-term phase of the trial. The mean number of wet nights per week decreased from a median of 5.3 (range 1.3-7.0) during the observation period to a median of 0.8 (range 0.0-5.0) during the last 3-mo period. Seventy-seven children became dry, 63 (83%) within 6 mo of treatment initiation. The percentage of children who became dry was similar in all age groups. Significantly fewer children in the lowest age group were defined as responders (52%; 95% CI 45, 59) among the 6-7-y-olds compared to 65% (56, 74) and 81% (72, 90) in the two older age groups. Desmopressin was well tolerated. No serious drug-related adverse events were recorded and no clinical symptoms of hyponatraemia were reported. The SWEET trial has demonstrated that desmopressin is both safe and effective for the long-term treatment of PMNE, with a significant therapeutic effect also in children of 6-7 y of age.