OBJECTIVE: To estimate the prevalence of primary nocturnal enuresis (PNE) in Taiwanese children, and to examine factors associated with PNE and its severity. SUBJECTS AND METHODS: In all, 1683 questionnaires were sent to parents of schoolchildren aged 6-11 years randomly selected from three primary schools in Taipei City, Taiwan. The questionnaire was designed to collect information about the prevalence of and factors associated with PNE. RESULTS: Of the questionnaires distributed, 1176 (70%) were completed. PNE was reported in 92 (8%) of the children; nine (10%) of these children were wet > 3 nights per week. Factors associated with PNE included male gender, deep sleep, divorced parents or separated family and a positive family history of enuresis. Of these factors, only those children with deep sleep were more likely to have > 3 wet nights per week. CONCLUSION: The prevalence of and factors associated with PNE in Taiwan are similar to those reported in Western countries, but the percentage of children with severe enuresis is lower than in Sweden, France and Turkey. Deep sleepers are more likely to have severe enuresis.