We investigated trends in the incidence of parkinsonism and Parkinson disease (PD) by comparing data from the first 2 subcohorts of the Rotterdam Study, a prospective, population-based cohort study (first subcohort: baseline 1990 with 10 years of follow-up; second subcohort, baseline 2000 with 10 years of follow-up). From the baseline years, we observed differences in the second subcohort that were associated with a lower risk of PD for some but not all baseline risk factors. Participants in both subcohorts were followed for a maximum of 10 years and monitored for the onset of parkinsonism, the onset of dementia, or death, until January 1, 2011. We used Poisson regression models to compare the incidences of parkinsonism, both overall and by cause (PD and secondary causes), and competitive events (incident dementia and death) as well as the mortality of parkinsonism patients in the 2 subcohorts. In the 1990 subcohort, there were 182 cases of parkinsonism (84 of which were PD) during 57,052 person-years. In the 2000 subcohort, we observed 28 cases of parkinsonism (10 with PD) during 22,307 person-years. The overall age- and sex-adjusted incidence of parkinsonism was lower in the 2000 subcohort (incidence rate ratio = 0.55, 95% confidence interval: 0.36, 0.81), and PD incidence declined sharply (incidence rate ratio = 0.39, 95% confidence interval: 0.19, 0.72). Competitive event rates were lower in the 2000 subcohort, and mortality rates among persons with parkinsonism remained stable. These findings suggest that the incidence of parkinsonism in general, and of PD in particular, decreased between 1990 and 2011.