The aim of this study was to contribute to differential diagnoses of unipolar and bipolar depression using cognitive variables of the Rorschach test (Comprehensive System).One hundred forty one depressed inpatients (71 bipolar, 70 unipolar; mean age = 46, SD = 15.8; 64% women) previously evaluated and comparable regarding clinical characteristics of their illness (including current mood symptoms) were blindly tested using the Rorschach test (C.S.).The cognitive profile of bipolar depressed patients was more impaired than the cognitive profile of unipolar depressed patients. Combining four cognitive specificities (tolerance to ambiguity, discrimination failure, difficulties in controlling ideational impulses, and impulsive or negligent processing) in a logistic regression model allows the identification of bipolarity with acceptable accuracy.Some aspects of cognitive functioning, as assessed with the Rorschach test (CS), appear to be useful to capture some important cognitive specificities of bipolar depression and could contribute to differential diagnoses of mood disorders.