We sought to assess the effect of the addition of a fixed dose of 5 mg daily of aripiprazole on hyperprolactinemia induced by risperidone long-acting injectable (RLAI) treatment in patients with chronic psychoses and the adverse events related to the addition of aripiprazole and its impact on the disease. This is an open uncontrolled clinical trial with 13 patients with a severe mental disorder (schizophrenia and other unspecified psychoses) treated with RLAI and with increased serum prolactin levels. Subjects received the addition of a fixed dose of 5 mg daily of aripiprazole for 3 months. The main efficacy outcome was the change in serum prolactin levels after 3 months of treatment. Twelve of the 13 patients showed a decrease in serum prolactin levels (81 ± 46 μg/L at baseline vs 42 ± 21 μg/L at month 1, P < 0.001, 52% mean reduction). In 2 patients, prolactin levels reverted normality. In 8 patients who continued treatment for 2 more months, the decrease in prolactin levels was maintained. Symptoms associated with hyperprolactinemia improved, and no worsening of the Clinical Global Impression Scale scores was observed. The adverse effects due to the addition of aripiprazole were mild and transient. The addition of aripiprazole 5 mg daily to RLAI was associated with a significant decrease in hyperprolactinemia levels and no major additional toxicity in patients with chronic psychosis.