To investigate the possible efficacy of amantadine in the control of pathological gambling (PG) associated with Parkinson disease (PD), 17 PD patients with PG were randomly selected for a double-blind crossover study with amantadine 200mg/day versus placebo and an open follow-up. Assessments included PG-specific scales (Yale-Brown Obsessive-Compulsive Scale for PG, Gambling-Symptom Assessment Scale, South Oaks Gambling Screen) and assessment of expenditures and time spent gambling. Amantadine abolished or reduced PG in all treated patients, as confirmed by scale score and daily expenditure reduction. Amantadine might be useful to treat PG. The effect of amantadine, acting as an antiglutamatergic agent, also opens new insights into the pathogenesis of PG.