The cognitive and behavioral symptoms of nonverbal learning disabilities (NLD) have been described by previous investigators. Nevertheless, we know far less about the potential genetic contributions that may predispose a child to have NLD. An endophenotype model was investigated in 5 samples of children ages 9 to 15 years: NLD (n = 32); reading disorders (RD; n = 59); participants with a psychiatric diagnosis but "without" a learning disability (n = 55); typically developing controls (n = 31); and children with velocardiofacial syndrome (VCFS), a chromosomal deletion syndrome that has been proposed as being an exemplar of NLD (VCFS + NLD; n = 20). Based on a family genetic interview, the authors' data suggest that children with NLD, RD, or a psychiatric diagnosis have a higher prevalence rate of attention-deficit/hyperactivity disorder (ADHD) and substance abuse/dependence. Psychiatric controls and children with NLD--but not children with RD--showed higher prevalence rates of familial bipolar disorder. (Contains 3 tables and 1 figure.)