Objective: The aim of this study was to determine the frequency of childhood ADHD comorbidity in patients with social anxiety disorder (SAD), and the influence of this comorbidity on various demographic and clinical variables in SAD. Method: A total of 130 patients with SAD were assessed with K-SADS-PL’s (Schedule for Affective Disorders and Schizophrenia for School-Age Children—Present and Lifetime Version) behavioral disorders module to determine the childhood diagnosis of ADHD. Patients with or without a comorbid childhood ADHD were compared in terms of clinical characteristics and rating scores. Results: The mean age at onset of SAD was lower, and lifetime major depressive disorder and bipolar disorder (BD) comorbidity were higher in the SAD–ADHD group than in the SAD–without ADHD group. Conclusion: We have found high ADHD comorbidity in patients with SAD. Presence of comorbid ADHD was associated with increased severity, functional impairment, and BD comorbidity.