The effect of readiness to change on treatment outcome was examined among 332 adolescents (46% male, 74% Caucasian), ages 12 through 17 years (M = 14.6, SD = 1.5), with major depressive disorder who were participating in the Treatment for Adolescents With Depression Study (TADS). TADS is a randomized clinical trial comparing the effectiveness of fluoxetine (an antidepressant medication), cognitive-behavioral therapy, their combination, and a pill placebo. An abbreviated Stages of Change Questionnaire was used to obtain 4 readiness to change scores: precontemplation, contemplation, action, and maintenance. The association between each readiness score and depression severity across 12 weeks of acute treatment for depression, as measured by the Children's Depression Rating Scale—Revised, was examined. Although treatment response was not moderated by any of the readiness scores, baseline action scores predicted outcome: Higher action scores were associated with better outcome regardless of treatment modality. Furthermore, treatment effects were mediated by change in action scores during the first 6 weeks of treatment, with increases in action scores related to greater improvement in depression. Assessing readiness to change may have implications for tailoring treatments for depressed adolescents.