CALM-PD (Comparison of the agonist pramipexole with levodopa on motor complications of Parkinson's disease) is a randomized, multicenter, double-blind, controlled clinical trial designed to compare the policy of initial treatment of pramipexole with the policy of initial treatment with levodopa in early, symptomatic Parkinson's disease with regard to the development of dopaminergic motor complications. At 22 American and Canadian sites, 301 eligible subjects requiring antiparkinsonian therapy to treat emerging disability were enrolled in CALM-PD and randomized to (i) active pramipexole and placebo levodopa or (ii) placebo pramipexole and active levodopa. Subjects are being evaluated systematically at regular intervals during a 23.5-month period to determine if and when dopaminergic motor complications (wearing off, dyskinesias, "on-off" effects) occur. In addition, quality-of-life outcomes, economic outcomes, and functional imaging outcomes are being assessed in standard fashion with [123I] beta-CIT and SPECT imaging throughout the trial. The study design contains many provisions to approximate routine clinical practice and to produce data about clinical effectiveness, tolerability, and cost to facilitate the evidence-based practice of neurology.