We estimated the prevalence of medication nonadherence in Parkinson's disease (PD) and the association between treatment nonadherence and healthcare costs. Insurance claims from over 30 US health plans were analyzed. Inclusion criteria were as follows: PD diagnosis, >or=1 PD-related prescription between 1/1/1997 and 12/31/2004, continuous health plan enrollment for >or=6 months before and >or=12 months after first PD prescription. Adherence, all-cause healthcare utilization, and all-cause costs were evaluated over 12 months post-treatment initiation. Adherence was measured using the medication possession ratio (MPR), with MPR
