The aim of this work was to investigate whether obesity and diabetes are related to risk of Parkinson's disease. We prospectively followed 147,096 participants in the Cancer Prevention Study II Nutrition Cohort from 1992 to 2005. Participants provided information on anthropometric variables and medical history at baseline and on waist circumference in 1997. Incident cases of Parkinson's disease (n = 656) were confirmed by treating neurologists and medical record review. Relative risks were estimated using proportional hazards models, adjusting for age, gender, smoking, and other risk factors. Neither body mass index nor waist circumference significantly predicted Parkinson's disease risk. Relative risk comparing individuals with a baseline body mass index of ≥30 to those with a body mass index <23 was 1.00 (95% confidence interval: 0.75, 1.34; P trend: 0.79), and that comparing individuals with a waist circumference in the top category (≥40.3 inches in men and ≥35 inches in women) to those in the bottom category (<34.5 inches in men and <28 inches in women) was 1.35 (95% confidence interval: 0.95, 1.93; P trend: 0.08). History of diabetes was not significantly associated with Parkinson's disease risk (combined relative risks = 0.88; 95% confidence interval: 0.62, 1.25; P heterogeneity = 0.96). In addition, neither body mass index at age 18 nor changes in weight between age 18 and baseline were significantly associated with Parkinson's disease risk. The results did not differ significantly by gender. Our results do not provide evidence for a relationship between body mass index, weight change, waist circumference, or baseline diabetes and risk of Parkinson's disease. © 2011 Movement Disorder Society