The present study sought to clarify the relevance of age of onset to the psychopathology of generalized anxiety disorder (GAD) using a large clinical sample of 154 patients with DSM-IV GAD. Most patients reported onset of GAD by early adulthood, although a smaller proportion of cases emerged in middle adulthood. Structural equation and regression models tested predictions that earlier onset GAD would be characterized by different levels of stress at disorder onset, disorder severity, lifetime comorbidity, and traits that predispose individuals to emotional disorders. Results showed that cases of GAD that emerged without any precipitating stressors were more likely to be of earlier onset. However, another-sizable group of patients with earlier-onset GAD identified severely stressful early environments that they linked to the emergence of GAD symptoms. In contrast, cases of GAD that began in adulthood were most likely to emerge in the context of mild to moderate stress. Further analyses revealed that earlier-onset GAD was associated with higher levels of disorder severity, comorbidity, and temperamental vulnerability to emotional disorders. These results are discussed in regard to their clinical and conceptual implications for anxiety disorders.