Based on the evidence that aripiprazole added to serotonin reuptake inhibitors (SRIs) or clomipramine in treatment-resistant obsessive-compulsive disorder (OCD) has reported promising results, the present 16-week, double-blind, randomized, placebo-controlled trial had the aim to explore the efficacy of aripiprazole add-on pharmacotherapy on clinical symptoms and cognitive functioning in a sample of treatment-resistant OCD patients receiving SRIs. After clinical and neurocognitive assessments, patients were randomly allocated to receive, in a double-blind design, 15 mg/d of aripiprazole or a placebo. A final sample of 30 patients completed the study. The results obtained indicate that aripiprazole added to stable SRI treatment substantially improved obsessive-compulsive symptoms as measured by changes on the Yale-Brown Obsessive Compulsive Scale total score and subscores (obsessions, P = 0.007; compulsions, P = 0.001; total score, P < 0.0001). Regarding cognitive functions, improvement was observed in some explored areas, such as attentional resistance to interference (Stroop score, P = 0.001) and executive functioning (perseverative errors, P = 0.015). The findings provide evidence that aripiprazole augmentation of SRIs/clomipramine treatment is well tolerated and may be proposed as an effective therapeutic strategy to improve outcome in treatment-resistant OCD.