To determine the longitudinal association of baseline body mass index and change in body mass index over 8 years to incident of patellofemoral osteoarthritis at the 8-year follow-up. A sample of 528 women and men, aged 45-65 years, with knee complaints and without radiographic evidence of patellofemoral and tibiofemoral osteoarthritis at baseline, were selected from the Cohort Hip and Cohort Knee cohort. Incidence of patellofemoral osteoarthritis was defined as presence of radiographic patellofemoral osteoarthritis (with or without tibiofemoral osteoarthritis) at the 8-year follow-up. Baseline body mass index data were categorized into normal, overweight, and obese weight-categories. Logistic regression analyses, adjusted for age and sex, were conducted to determine the association of baseline body mass index and change in body mass index to patellofemoral osteoarthritis incidence 8 years later. Obesity was associated with greater odds of radiographic patellofemoral osteoarthritis incident (odds ratio: 1.8 [95% CI 1.1, 3.1]) 8 years later. There were no significant associations observed between body mass index change over 8 years and incidence of radiographic patellofemoral osteoarthritis in overweight and obese individuals. Obesity is associated with increased odds of developing radiographic patellofemoral osteoarthritis 8 years later.