ADHD and incontinence are common childhood disorders which co-occur at much higher rates than expected by chance. The aim of this review was to provide an overview both of the comorbidity of nocturnal enuresis (NE), daytime urinary incontinence (DUI) and faecal incontinence (FI) in children with ADHD; and, vice versa, of the co-occurrence of ADHD in children with NE, DUI and FI. Most clinical studies have focussed on the association of ADHD and NE. Population-based studies have shown that children with DUI have an even greater risk for ADHD than those with NE. While children with FI have the highest overall comorbidity rates of psychological disorders, these are heterogeneous with a wide range of internalising and externalising disorders--not necessarily of ADHD. Genetic studies indicate that ADHD and NE, DUI and FI do not share the same genetic basis. The comorbidity is conferred by non-genetic factors. Possible aetiological and pathogenetic links between ADHD and incontinence are provided by neurophysiological, imaging and pharmacological studies. The co-occurrence has clinical implications: children with ADHD and NE, DUI and FI are more difficult to treat, show lower compliance and have less favourable treatment outcomes for incontinence. Therefore, both groups of disorders have to be assessed and treated specifically.