Objectives. This study determined whether the incidence of diabetes is reduced among physically active older women. Methods. We assessed physical activity by mailed questionnaire and 12-year incidence (ostensibly type 2 diabetes) in a cohort of 34257 women aged 55 to 69 years. Results. After adjustment for age, education, smoking, alcohol intake, estrogen use, dietary variables, and family history of diabetes, women who reported any physical activity had a relative risk of diabetes of 0.69 (95% confidence interval = 0.63, 0.77) compared with sedentary women. Conclusions. These findings suggest that physical activity is important for type 2 diabetes prevention among older women.