The present study aimed to examine the relevance of age of onset to the psychopathology of social phobia using a large clinical sample of 210 patients with social phobia. The two most common periods of onset were during adolescence (ages 14–17) and early childhood (prior to age 10). Structural regression modeling was used to test predictions that early onset social phobia would be associated with greater severity of the disorder, stronger current symptoms of depression and anxiety, greater functional impairment, and more pronounced levels of emotional disorder vulnerabilities (e.g., neuroticism/behavioral inhibition, extraversion, perceptions of control). Logistic regression was used to evaluate relationships between age of onset and the presence of acute and chronic stress at the time of onset. Results showed that earlier age of social phobia onset was associated with stronger current psychopathology, functional impairment, and emotional disorder vulnerabilities, and that later age of onset predicted the presence of an acutely stressful event around the time of disorder emergence. These results are discussed in regard to their clinical implications and congruence with prominent etiological models of the emotional disorders.