OBJECTIVE To determine the epidemiology, clinical characteristics and natural history of nursing home residents with a diagnosis of Parkinson's disease (PD). METHODS A cohort study with 18-month follow-up utilizing resident assessments from the National HealthCorp 1991-1992 dataset. METHODS Seventy-one National HealthCorp nursing homes. METHODS A total of 5020 nursing home residents older than age 55 were studied. Residents with primary and secondary diagnoses of PD were identified from the population using the International Classification of Diseases, Ninth Revision, Clinical Modification code 332.0. METHODS Baseline demographic and clinical characteristics were compared for residents with and those without Parkinson's disease. Outcome measures over the course of 18 months included death and functional status. RESULTS The prevalence of a diagnosis of PD was 6.8%. Significant factors associated independently with PD included: younger age (79 +/- 7 vs 81 +/- 9 years; P < .001), male sex (32% vs 23%; P < .001), severe dependence in activities of daily living (OR = 1.26; 95% CI 1.08-1.46), impared body control (OR = 1.38; 95% CI 1.03-1.68), symptoms of depression (OR = 1.29; 95% CI 1.02-1.64), and the number of daily medications (OR = 1.23; 95% CI 1.08-1.44). Residents with a diagnosis of PD had a faster rate of functional decline over 18 months (P < .001) but did not have a higher mortality rate than residents without PD. CONCLUSIONS Parkinson's disease is a relatively common diagnosis among nursing home residents and is associated with increased functional disability. There are several potentially modifiable conditions associated with PD that may offer an opportunity to design specific interventions and health services to improve the quality of life and slow functional decline in this frail population.