The impact of weight change on diabetes incidence remains unclear. To clarify the role of weight change as a risk factor for diabetes, the authors assessed the association between weight change and diabetes incidence conditional upon either initial or attained body mass index (BMI). They used 7,837 observations available from repeated measurements of 4,259 participants (men and women aged 20-59 years) in the Dutch population-based Doetinchem Cohort Study (1987-2007) to analyze the association between 5-year weight change and diabetes incidence (n = 124) in the subsequent 5 years. When adjusted for initial BMI, 5-year weight change was a significant risk factor for diabetes (odds ratio = 1.08, 95% confidence interval: 1.04, 1.13 per kilogram of weight change). However, no significant association was found between weight change and diabetes if the association was adjusted for attained BMI (odds ratio = 0.99, 95% confidence interval: 0.94, 1.04 per kilogram of weight change). Results suggest that weight change is associated with diabetes incidence because, conditional upon initial BMI, weight change determines attained BMI. This finding implies that lifestyle interventions can contribute to diabetes prevention because they affect attained BMI. Weight change appears to have no effect on diabetes incidence beyond its effect on attained BMI.