Lack of treatment response is a critical problem in major depressive disorder (MDD). Cariprazine is a D3-preferring dopamine D3/D2 receptor partial agonist and 5-HT1A partial agonist. This phase 3, multicenter, open-label, long-term (26-week), flexible-dose (1.5-4.5 mg/day) study assessed the long-term safety and tolerability of cariprazine used adjunctively with antidepressant therapy in adult patients with MDD who had either completed a lead-in study (n=311) or had been newly recruited (n=131). A higher percentage of continuing patients (66.2%) than new patients (35.9%) completed the study. The most common reason for discontinuation was adverse events (AEs; 13.9%); 79% of patients experienced a treatment-emergent AE [most common: akathisia (15.9%,) headache (11.6%)]. Serious AEs occurred in 2% of patients; two deaths occurred (one traffic accident, one completed suicide, both considered unrelated to treatment). The mean changes in clinical laboratory, cardiovascular, and ophthalmologic parameters were generally not clinically relevant. The mean (SD) changes from the open-label baseline in Montgomery-Åsberg Depression Rating Scale total score and Clinical Global Impression-Severity score at week 26 were -7.3 (9.5) and -1.0 (1.2), respectively. By week 26, 53.3% of patients were in remission (Montgomery-Åsberg Depression Rating Scale total score≤10). The results suggest that cariprazine was generally safe and well tolerated as adjunctive therapy to treat MDD.