PURPOSE. The purpose of the study was to describe the prevalence, severity, and associated risk factors for pterygium in a population-based sample of rural residents of the Bai minority population in rural Dali, China. METHODS. A population-based survey of Chinese Bai Nationality aged 50 years from randomly selected block groups in southwestern China was conducted. A clinical examination by experienced ophthalmologists was carried out, and the presence of pterygium was diagnosed at the examination. Pterygium was graded clinically by slit lamp examination. Questionnaires were conducted on risk factors. RESULTS. From a total of 2742 eligible subjects, 2133 (77.8%) were examined. The prevalence of pterygium was high (overall 39.0% [95% confidence interval (CI) 37.0-41.0]). Women had a higher rate than men (27.3% vs. 11.7%, respectively). In multivariate analysis, pterygium was independently associated with increasing age (odds ratio [OR] 1.55 [95% CI 1.24-1.93], 1.47 [95% CI 1.13-1.91], and 1.79 [95% CI 1.17-2.73], respectively, for persons 60-69 years, 70-79 years, and 80 years and older compared with 50-59 years), female sex (OR 1.42 [95% CI 1.08-1.88]), lack of formal education (OR 1.26 [95% CI 1.03-1.56]), and presence of outdoor work (OR 1.51 [95% CI 1.10-1.92]). Height, weight, hypertension, diabetes, smoking, and alcohol use history were not associated with pterygium. CONCLUSIONS. The prevalence of pterygium in Dali is 39.0% among Chinese Bai aged 50 years and older. Independent associations with increasing age (> 59 years), female sex, lack of education, and occupations linked to outdoor work suggest a multifactorial cause of this condition. (Invest Ophthalmol Vis Sci. 2012;53:6617-6621) DOI:10.1167/iovs.11-8947