Data on the efficacy of quetiapine in borderline personality disorder (BPD) are still scarce. We aimed to investigate the efficacy of quetiapine for impulsivity and a broad range of affective symptoms in BPD. In this 12-week open-label study, we included individuals with BPD who presented to psychiatric in- and outpatient services. After a gradual titration of quetiapine, a flexible dose (range, 100-800 mg) was administered. The main outcome measures consisted of the scores on patient-rated questionnaires (Barratt Impulsiveness Scale, Buss-Durkee Hostility Inventory, Affective Lability Scale, Spielberger State and Trait Anxiety Inventory, Spielberger State and Trait Anger Inventory, and Beck Depression Inventory) and on neurocognitive tasks related to impulsivity (Stroop Color Word Task and IOWA Gambling Task). A mixed linear model, correcting for age, sex, antidepressant use, and weeks in psychotherapy, was applied. Forty-one patients (34 females and 7 males; mean [SD] age, 27.0 [9.0] years) were enrolled in the study, 32 of which completed the trial. Patients' scores decreased significantly (mean [SD] difference; P value) on the Barratt Impulsiveness Scale (19.7 [2.0]; P < 0.0001), Buss-Durkee Hostility Inventory (11.5 [1.4]; P < 0.0001), Affective Lability Scale (0.75 [0.08]; P < 0.0001), Beck Depression Inventory (25.0 [1.7]; P < 0.0001), Spielberger State and Trait Anxiety Inventory state (19.9 [1.9]; P < 0.0001) and trait (20.8 [1.7]; P < 0.0001) subscale, and Spielberger State and Trait Anger Inventory state (7.3 [1.1]; P < 0.0001) and trait (10.1 [1.0]; P < 0.0001) subscale. In addition, patients showed significantly less inference on the Stroop Color Word Task and had more 'good choices' on the IOWA Gambling Task. These results suggest that quetiapine may be efficacious in the treatment of impulsivity and affective symptoms in BPD.