Data from a community epidemiological study of 1,869 families (Ontario Child Health Study) was used to evaluate the effect of different ways of operationalizing DSM-III-R criteria for overanxious disorder (OAD) and separation anxiety disorder (SAD) among adolescents aged 12 to 16. The authors determined that a high threshold for symptoms to qualify as present, the presence of one or both of the essential symptoms, and the presence of four or more auxiliary symptoms for OAD and three or more for SAD gave prevalence of OAD of 3.6% and SAD of 2.4%. There was high overlap between the presence of OAD and SAD and externalizing disorder and depression, but one-half of youth with OAD and SAD had pure anxiety disorder. Youth with OAD and SAD were just as impaired as youth with externalizing disorder and depression, except that they admitted to less social isolation and their schoolwork was less affected.