Pathological gambling (PG) is a potential complication related to the treatment of Parkinson disease (PD) with dopamine agonists(DA). The cause of this disorder is unknown, but altered dopamine neurotransmission may be involved. Objective: We evaluated the efficacy and tolerability of the opioid antagonist naltrexone in the treatment of PG in PD. Methods: Our cases included 3 patients with PD who developed PG after DA treatment. Results: Pathological gambling did not improve after reduction or discontinuation of DA. These patients responded poorly to serotonin reuptake inhibitors, whereas treatment with opioid antagonist naltrexone resulted in the remission of PG. Naltrexone treatment was well tolerated. In one patient, higher dose of naltrexone resulted in hepatic abnormalities, which resolved after dosage reduction. Conclusions: The opioid antagonist naltrexone could be an effective option for the treatment of PG in PD.