A study on the familial background of nocturnal enuresis was conducted by administering a questionnaire to all school children in 1st year of Elementary Education. A total of 4,425 children were surveyed. The number of questionnaires returned was 2,770. Only 2,616 children born in 1985, aged 6-7 years, with no schooling delay were evaluated. A familial background of enuresis is much more frequent in enuretic than non-enuretic children (p < 0.001). When NE existed in first degree relatives, enuresis was also present in up to 40% children versus 8.5% in those with no familial history (p < 0.001). The background of NE is the father in 39.6% enuretic and 8.2% non-enuretic children (p < 0.001); in 42.1% enuretic children NE background was the mother, while non-enuretic children have maternal background in 10.4% (p < 0.001). Children with NE have a background of enuresis in their siblings in 62.9% cases versus 20.9% of non-enuretic children (p < 0.001).