The objective of the current study was to identify the associations between phenotype and genotype in children with nocturnal enuresis. Of the total of 167 wetting children, aged 5-10 years, without neurological or structural forms of incontinence, 110 were nocturnal enuretics. The examinations included a full psychiatric and psychological assessment, a paediatric and neurological examination, a family history with pedigree, ultrasonography, uroflowmetery, urinanalysis and bacteriology. Children with secondary nocturnal enuresis (n = 28) had a significantly higher rate of behavioural disorders, life events and continuous psychosocial stress than those with primary nocturnal enuresis (n = 82). Of the latter group, children with primary monosymptomatic nocturnal enuresis (n = 50) had an especially low rate of behavioural problems, when in comparison to primary non-monosymptomatic nocturnal enuretics (n = 32). Formal genetics point to a high genetic predisposition to nocturnal enuresis in all subgroups. Linkage studies to markers on chromosomes 8, 12 and 13 demonstrate both clinical, as well as genetic heterogeneity in nocturnal enuresis.