This study examined whether patients' expectations of treatment outcome predict treatment completion, homework compliance, and depressive symptom improvement in cognitive behavior therapy (CBT) and mindfulness-based cognitive therapy (MBCT). Study participants were patients with diabetes and comorbid depressive symptoms who were randomized to 8 sessions of either CBT (n = 45) or MBCT (n = 46), both individually delivered. The results showed that high outcome expectations were predictive of post-treatment depressive symptoms in CBT and MBCT, but not of early and mid-treatment symptoms. Patients' outcome expectations predicted treatment completion in CBT and MBCT as well as homework compliance in MBCT. Homework compliance did not mediate the association between patients' outcome expectations and post-treatment depressive symptom improvement. The findings do not support the hypothesis that patients' expectations have an immediate impact on patients' mental state and partially support the notion that patients are less involved in treatment when they hold low expectations for improvement.