To study whether being diagnosed with a cardiovascular disease (CVD) or diabetes mellitus (DM) is associated with improvements in lifestyles.We used data from the Doetinchem Cohort Study, a prospective study among 6386 Dutch men and women initially aged 20–59years who were examined four times over 15years (1987–2007). Logistic and linear regression models were used to assess the effect of a self-reported diagnosis of CVD (n=403) or DM (n=221) on smoking, alcohol consumption, weight, diet and physical activity.Self-reported diagnosis of CVD increased rates of smoking cessation (OR=2.2, 95%CI 1.6 – 3.1). Adults reporting a diagnosis of DM (relatively) decreased weight (3.2%, 95%CI 2.2 – 4.2), (relatively) decreased energy intake (4.2%, 95%CI 0.7 – 7.7), decreased energy percentage from saturated fat (0.4%, 95%CI 0.0 – 0.9) and increased fish consumption (2.8 g/day, 95%CI 0.4 – 5.1). A self-reported diagnosis of CVD or DM was not associated with changes in physical activity.A diagnosis of CVD or DM may act, along with possible effects of medical treatment, as a trigger to adopt a healthier lifestyle in terms of smoking cessation, healthier diet and weight loss.