Background: Few studies have examined the long-term effect of habitual diet on risks of incident diabetes, coronary heart disease, and mortality. Objective: We analyzed the prospective relation of dietary patterns with incident chronic disease and mortality during 15 y of follow-up in the Whitehall II study. Design: We conducted a prospective analysis (106 633 person-years at risk) among men and women (n = 7731) with a mean age of 50 y at the time of dietary assessment (127-item food-frequency questionnaire). Coronary death or nonfatal myocardial infarction and incident diabetes were verified by record tracing and oral-glucose-tolerance tests. Results: Cluster analysis identified 4 dietary patterns at baseline. The patterns were termed unhealthy (white bread, processed meat, fries, and full-cream milk; n = 2665), sweet (white bread, biscuits, cakes, processed meat, and high-fat dairy products; n = 1042), Mediterranean-like (fruit, vegetables, rice, pasta, and wine; n = 1361), and healthy (fruit, vegetables, whole-meal bread, low-fat dairy, and little alcohol; n = 2663). Compared with the unhealthy pattern, the healthy pattern reduced the risk of coronary death or nonfatal myocardial infarction and diabetes; hazard ratios (95% CI) were 0.71 (0.51, 0.98) and 0.74 (0.58, 0.94), respectively, after adjustment for age, sex, ethnicity, dietary energy misreporting, social position, smoking status, and leisure-time physical activity. Dietary pattern was not associated with all-cause mortality. Residual confounding by socioeconomic factors was unlikely to account for the observed dietary effects. Conclusions: The healthy eating pattern reduced risks of diabetes and major coronary events. Such dietary patterns offer considerable health benefits to individuals and contribute to public health.