Using family study methodology and assessments made by blind raters, this study evaluated family-genetic and psychosocial risk factors for DSM-III attention deficit disorder (ADD) among the 457 first-degree relatives of clinically referred children and adolescents with ADD (N = 73), compared with psychiatric (N = 26) and normal controls (N = 26). Relatives of ADD probands had a higher morbidity risk for ADD (25.1% versus 5.3% versus 4.6%, ps less than 0.00001), antisocial disorders (25.3% versus 6.9% versus 4.2%, ps less than 0.00001), and mood disorders (27.1% versus 13.9%, p = 0.038 and 27.1% versus 3.6%, p = 0.00001) than did relatives of psychiatric and normal controls. The increased risk for ADD could not be accounted for by gender or generation of relative, the age of proband, social class, or the intactness of the family. These results confirm and extend previous findings indicating important family-genetic risk factors in ADD.