Résumé : This study is the first investigation to identify clinical factors associated with treatment resistance in bipolar depression (TRBD). TRBD is defined as failure to respond to at least two consecutive adequate antidepressant trials. The primary objective of this European Multicenter Study was to identify specific clinical and demographic factors associated with TRBD in a sample of bipolar patients treated for a major depressive episode. A total of 261 bipolar patients with major depressive episode were included in the analysis. Among them, 162 patients were considered as responders to treatment and the remaining 99 patients were considered as treatment resistant with a 17-item Hamilton Rating Scale for Depression Score remaining superior or equal to 17 after two consecutive adequate antidepressant trials. Cox regression analysis was used to examine the association between individual clinical variables and TRBD. We found four clinical variables to be significantly associated with TRBD: melancholia [P=0.01, odds ratio (OR)=2.4], comorbidity with social phobia (P=0.02, OR=2.3), current suicidal risk (P=0.02, OR=1.8) and severe intensity of current depressive episode (P=0.01, OR=1.8). Our findings identify four clinical variables associated with TRBD, which could be further investigated in controlled prospective trials.