Even with optimal therapy, it is inevitable that the symptoms of Parkinson's disease (PD) progress and gradually result in disability in the performance of daily activities. Delay and prevention of disability is among the highest priorities in the clinical management of PD. Understanding the association between the diverse symptoms of PD and the emerging disability is fundamental to minimizing functional limitations. This article differentiates disability from impairment and quality of life and explores the relationship between the specific impairments of PD and resulting disability. Identifying appropriate tools for outcomes measurement and impediments to accurate assessment of disability are also reviewed.