Background: There is growing evidence suggesting that early adversity may be a marker for a distinct pathway to major depressive disorder (MDD). We examined associations between childhood adversity and a broad variety of clinical characteristics and response to pharmacotherapy in a large sample of patients with chronic forms of MDD. Methods: Subjects included 808 patients with chronic forms of MDD (chronic MDD, double depression, or recurrent MDD with incomplete recovery between episodes and a total continuous duration of >2 years) who were enrolled in a 12-week open-label trial of algorithm-guided pharmacotherapy. Baseline assessments included a semi-structured diagnostic interview, and clinician- and self-rated measures of depressive symptoms, social functioning, depressotypic cognitions, and personality traits, and childhood adversity. Patients were re-evaluated every 2 weeks. Results: A longer duration of illness; earlier onset; greater number of episodes, symptom severity, self-rated functional impairment, suicidality, and comorbid anxiety disorder; and higher levels of dysfunctional attitudes and self-criticism were each associated with multiple forms of childhood adversity. A history of maternal overcontrol, paternal abuse, paternal indifference, sexual abuse, and an index of clinically significant abuse each predicted a lower probability of remission. Among patients completing the 12-week trial, 32% with a history of clinically significant abuse, compared to 44% without such a history, achieved remission. Conclusions: These findings indicate that a history of childhood adversity is associated with an especially chronic form of MDD that is less responsive to antidepressant pharmacotherapy. Depression and Anxiety, 2009. Published 2009 Wiley-Liss, Inc.