In order to better understand individual vulnerabilities to bipolar I disorder, our study evaluates individual differences in Behavioral Activation and Inhibition Systems as possible markers of bipolar I disorder. We evaluated BAS and BIS functioning in 39 bipolar I euthymic patients and in 38 controls. Patients showed higher scores on the BAS scale while differences weren't detected on the BIS scale. Eighteen months after the initial assessment, patients were re-grouped according to the presence and type of new affective episodes. Those relapsing with a depressive episode showed lower scores on the BAS scale than patients suffering from a manic/hypomanic episode, and a tendency to score lower than patients still asymptomatic. The reported higher BAS functioning would reinforce the hypothesis of a trait vulnerability to present approach behaviors during euthymia associated with bipolar I disorder, not necessarily related to the proximity of a manic/hypomanic episode, and interestingly not detected when approaching a depressive episode, circumstance in which BAS functioning would be similar to controls. Results didn't reveal a weaker BIS in patients, hypothesized to account for BAS instability in bipolar I disorder.