Twenty patients with problematic restless legs syndrome (RLS) were treated with pergolide. Efficacy, dosage, side effects, and tolerance were analyzed. Fifteen patients continued treatment for a median study time of 2 years. Five patients discontinued treatment after a mean of 4.2 months. Pergolide resulted in complete or near complete control of symptoms in 45% and moderate control in 50% of patients studied. Levodopa-induced daytime augmentation resolved in all patients in whom it had been present. The mean total daily maintenance dose of pergolide was 0.23 mg. Forty percent required an additional afternoon dose. Side effects developed in 12 patients (60%) and necessitated discontinuation of treatment in five. Common side effects were nausea, dizziness, and insomnia. Daytime augmentation occurred in 27% of patients, but this was mild and usually easily controlled with a supplementary afternoon dose of pergolide. Tolerance did not develop. We conclude that pergolide is an effective second-line agent for RLS, especially following levodopa-induced daytime augmentation.