Purpose: To measure the incidence of pars planitis in a community-based population and to report clinical features, complications, and visual prognosis. Design: Population-based, retrospective, 20-year cohort study. Methods: Multicenter study using the Rochester Epidemiology Project medical records linkage system, which allows analysis of almost all patients within Olmsted County, Minnesota, with a given medical condition. Databases were searched to identify all patients with pars planitis from January 1, 1985 through December 31, 2004. Forty-six eyes of 25 patients were evaluated. Results: Mean follow-up was 14.3 years. The incidence of pars planitis was 2.077 per 100,000 persons (95% confidence interval [CI], 1.43 to 2.62). The most common complications were epiretinal membrane (ERM) in 17 eyes (36%), cataract in 14 eyes (30.4%), and cystoid macular edema (CME) in 12 eyes (26.1%). Mean visual acuity after 10 years of follow-up was 20/30, with 18 of 24 patients maintaining a visual acuity of 20/40 or better. One-third of patients maintained normal visual acuity without requiring treatment. Conclusions: The visual prognosis of pars planitis is relatively good, with 75% of patients maintaining a visual acuity of 20/40 or better after 10 years. Many patients with mild disease do not require treatment. A subset of patients, however, experience severe disease with severe vision loss despite treatment. The rate of smoking and multiple sclerosis in patients with pars planitis is much higher than that of the general population.