Rumination involves a repetitive, passive focus on one’s thoughts and feelings and has been hypothesized as a mechanism contributing to multiple psychopathologies. The current investigation explores secondary outcomes from a pilot study to examine whether rumination-focused cognitive behavior therapy (RFCBT) alleviates symptoms of anxiety, increases behavioral activation, or increases global functioning among adolescents with a history of Major Depressive Disorder (MDD). Thirty-three adolescents were randomized to receive either RFCBT (n = 17) or assessment only (AO; n = 16) over the course of eight weeks. Mixed effects regression models were used to conduct intent-to-treat (ITT) analyses. The quadratic interaction for group-by-time-by-time was significant for anxiety. Adolescents in the RFCBT group experienced a significant decrease in anxiety across the first six weeks of intervention (F = 7.01, df = 108.49, p = 0.009). The group-by-time interaction was significant for the behavioral activation outcome (F = 4.28, df = 25.60, p = 0.049) with youth randomized to RFCBT demonstrating increasing activation compared to AO. Global functioning did not significantly differ between groups (F = 0.40, df = 1, p > 0.05). Preliminary evidence suggests that RFCBT may hold promise as an intervention that alleviates both depressive and anxiety symptoms when comorbid.