During retrospective and prospective studies, we attempted to determine the clinical characteristics, treatment, and visual outcome of patients with pars planitis and to evaluate the association between pars planitis and multiple sclerosis (MS). The retrospective study included 44 patients with pars planitis, who had been examined between October 1986 and January 1999. We analyzed age, sex, visual acuity (VA), median follow-up time, and medical and surgical treatments. The prospective study, which included 21 consecutive patients with pars planitis, was performed to determine the presence of MS. In the retrospective study, the mean patient age was 22.4 years (SD +/- 11.5) and the median follow-up was 34.9 months (SD +/- 27.2). Complications included macular edema (47.7%), vitreous opacities (38.6%), papillitis (38.6%), vasculitis (36.4%), and cataract (20.5%). Forty patients (90.9%) had a final bilateral VA better than 20/40. In the prospective study, magnetic resonance imaging (MRI) was performed. Demyelinating lesions were found in 10 (47.6%) of the 21 patients and relapsing-remitting clinically definite MS was diagnosed in seven (33.3%). With the exception of age, no significantly statistical differences were observed when the visual prognosis and the clinical and epidemiologic characteristics were compared between the two groups of patients with and without associated MS; a diagnosis of MS was more frequently made in patients over 25 years of age. With appropriate treatment, patients with pars planitis have a good visual prognosis. Because the presence of demyelinating lesions seems to be high among patients with pars planitis, MRI should be considered, especially in patients over 25 years of age.