Background: Depressed individuals often exhibit impaired inhibition to negative input and identification of positive stimuli, but it is unclear whether this is a state or trait feature. We here exploited a naturalistic model, namely individuals with seasonal affective disorder (SAD), to study this feature longitudinally. Aim: The goal of this study was to examine seasonal changes in inhibitory control and identification of emotional faces in individuals with SAD. Method: Twenty-nine individuals diagnosed with winter-SAD and 30 demographically matched controls with no seasonality symptoms completed an emotional Go/NoGo task, requiring inhibition of prepotent responses to emotional facial expressions and an emotional face identification task twice, in winter and summer. Results: In winter, individuals with SAD showed impaired ability to inhibit responses to angry (p = .0006) and sad faces (p = .011), and decreased identification of happy faces (p = .032) compared with controls. In summer, individuals with SAD and controls performed similarly on these tasks (ps > .24). Conclusion: We provide novel evidence that inhibition of angry and sad faces and identification of happy faces are impaired in SAD in the symptomatic phase, but not in the remitted phase. The affective biases in cognitive processing constitute state-dependent features of SAD. Our data show that reinstatement of a normal affective cognition should be possible and would constitute a major goal in psychiatric treatment to improve the quality of life for these patients.