Nearly all studies on the co-morbidity between enuresis and psychopathology in children suggest an increased prevalence of behavioural disorders in general and of attention-deficit hyperactivity disorder (ADHD) in particular. Depending strongly on characteristics of the study design, the extent to which this prevalence is increased fluctuates heavily. In the current literature review we found a lack of standardization in the definitions of both enuresis and psychopathology, which makes comparison of research findings difficult. A series of confounding factors that possibly bias study results is also covered. Psychopathology in enuresis seems to be associated with older age, male gender, low socio-economic status and admission to specialized (university) paediatric clinics. Research that fails to report or to control for these factors will not be able to make generalizations to the total population of enuretic children. It is highly important for paediatricians to be aware of the effect of these methodological factors in order to read critically and appreciate the co-morbidity studies on the one hand and to understand better the association between enuresis and psychopathology on the other hand. Future research would benefit from diagnoses based on international diagnostic classification systems made within a well-defined sample.