Objectives: The present study investigates the role of dysfunctional cognitions in patients with chronic tinnitus. To explore different dimensions of tinnitus-related thoughts, a 22-item self-report measure, the Tinnitus Cognitions Scale (T-Cog), is presented. Furthermore, dysfunctional cognitions are examined as a possible mediator of the relation between tinnitus distress and depression. Design: The present study analyzes the cross-sectional data of 373 patients with chronic tinnitus. Parallel analysis and principal axis factoring are used to identify the factor structure of the T-Cog. Assumed mediating effects are tested using the asymptotic and resampling procedure. Results: Factor analysis reveals two factors interpreted as tinnitus-related catastrophic thinking and tinnitus-related avoidance cognitions. Internal consistency is sufficient with a Cronbachs of 0.88 for the total scale and 0.74 and 0.87 for the subscales. The authors find high associations between the T-Cog and other measures of tinnitus distress, depression, anxiety, and tinnitus acceptance, indicating convergent validity. With the exception of neuroticism, low correlations with personality factors are found, indicating discriminant validity. Patients with moderate or severe tinnitus distress report significantly higher scores of dysfunctional cognitions than patients with mild tinnitus distress. Tinnitus-related catastrophic thinking and tinnitus-related avoidance cognitions partially mediate the relation between tinnitus distress and depression. Conclusions: Dysfunctional cognitions can play an important role in the degree of tinnitus distress. Catastrophic and avoidant thoughts contribute to the explanation of depression among tinnitus patients. The T-Cog is a reliable and valid questionnaire for the assessment of different dimensions of cognitions. Its use could provide information for identifying tinnitus patients who are particularly suitable for cognitive-behavioral therapy.