There is no empirical basis for determining which seasonal affective disorder (SAD) patients are best suited for what type of treatment. Using data from a parent clinical trial comparing light therapy (LT), cognitive-behavioral therapy (CBT), and their combination (CBT + LT) for SAD, we constructed hierarchical linear regression models to explore baseline cognitive vulnerability constructs (i.e., dysfunctional attitudes, negative automatic thoughts, response styles) as prognostic and prescriptive factors of acute and next winter depression outcomes. Cognitive constructs did not predict or moderate acute treatment outcomes. Baseline dysfunctional attitudes and negative automatic thoughts were prescriptive of next winter treatment outcomes. Participants with higher baseline levels of dysfunctional attitudes and negative automatic thoughts had less severe depression the next winter if treated with CBT than if treated with LT. In addition, participants randomized to solo LT who scored at or above the sample mean on these cognitive measures at baseline had more severe depressive symptoms the next winter relative to those who scored below the mean. Baseline dysfunctional attitudes and negative automatic thoughts did not predict treatment outcomes in participants assigned to solo CBT or CBT + LT. Therefore, SAD patients with extremely rigid cognitions did not fare as well in the subsequent winter if treated initially with solo LT. Such patients may be better suited for initial treatment with CBT, which directly targets cognitive vulnerability processes.