This study evaluated the treatment effects of Behavioral Activation (BA) on adolescents with major depressive disorder (MDD). A total of 28 adolescents (M age = 15.43) participated in this 18‐week study. Semi‐structured diagnostic interviews were used to determine depression status. Multiple informant methods (participants, parents, therapists, independent assessors) evaluated clinical change. Assessments were conducted at baseline, midpoint, end of treatment, and 3‐ and 6‐month follow‐ups. Results suggested that BA was an effective treatment for depressed adolescents. At the end of treatment, 90.9% of completers no longer met criteria for MDD, with 54.5% classified as fully remitted, 36.4% classified as responders, and only 9.1% classified as nonresponders. Follow‐up assessments indicated that treatment effects were sustained. Conclusions and future directions are discussed.