OBJECTIVE: We sought to establish prevalence rates and detail patterns of comorbidity for generalized anxiety disorder, separation anxiety disorder, and social phobia in preschool-aged children. METHOD: The Duke Preschool Anxiety Study, a screen-stratified, cross-sectional study, drew from pediatric primary care and oversampled for children at risk for anxiety. A total of 917 parents of preschool children (aged 2-5 years) completed the Preschool Age Psychiatric Assessment. RESULTS: Generalized anxiety disorder, separation anxiety disorder, and social phobia are common in preschool-aged children attending pediatric primary care. Three-fourths of preschoolers with an anxiety disorder only had a single anxiety disorder. Generalized anxiety disorder displayed the greatest degree of comorbidity: with separation anxiety disorder (odds ratio [OR] = 4.1, 95% CI = 2.0-8.5), social phobia (OR = 6.4, 95% CI = 3.1-13.4), disruptive behavior disorders (OR = 5.1, 95% CI = 1.6-15.8), and depression (OR = 3.7, 95% CI = 1.1-12.4). CONCLUSIONS: The weakness of association between generalized anxiety disorder and depression stands in contrast to substantial associations between these 2 disorders reported in older individuals. Attenuated associations in preschool-aged children could translate into clinical opportunities for targeted early interventions, aimed at modifying the developmental trajectory of anxiety disorders.