BACKGROUND Pathological gambling is a rare potential complication related to treatment of Parkinson disease (PD). However, the etiology of this behavior is poorly understood. OBJECTIVE To examine the relationship between medical therapy for PD and pathological gambling. METHODS In our routine movement disorders practice (2002-2004), we encountered 11 patients with idiopathic PD who had recently developed pathological gambling. We assessed the relationship to their medical therapy and compared them with cases identified by systematic review of the existing literature on pathological gambling and PD. RESULTS All 11 patients with PD and pathological gambling were taking therapeutic doses of a dopamine agonist; 3 of these patients were not treated with levodopa. In 7 patients, pathological gambling developed within 3 months of starting to take or escalating the dose of the agonist; in the other 4 with a longer latency, gambling resolved after the agonist use was discontinued. Pramipexole dihydrochloride was the agonist in 9 of 11 cases in our series and 10 of 17 in the literature (68% in total). CONCLUSIONS Dopamine agonist therapy was associated with potentially reversible pathological gambling, and pramipexole was the medication predominantly implicated. This may relate to disproportionate stimulation of dopamine D(3) receptors, which are primarily localized to the limbic system.