Background: Health behavior theories suggest that occurrence of heart attack or stroke in an immediate family member should increase one's perceived susceptibility to these conditions, which might lead to improved risk factor behavior and control. Methods: Changes in measures of smoking, physical activity, lipids/lipoproteins, body weight, and blood pressure were investigated over two consecutive 5-year follow-up periods among 3950 participants (aged 18 to 30 years) in the Coronary Artery Risk Development in Young Adults (CARDIA) study, who either did or did not have an immediate family member experience a heart attack or stroke. Recruitment and examinations for Years 0, 5, and 10 took place in 1985-1986, 1990-1991, and 1995-1996, respectively. Results: After adjustment for baseline demographics and risk factors, young adults who experienced a change in family history of heart attack or stroke over a 5-year period were no more likely than those who did not to quit smoking, or to experience more positive changes in weight, physical activity, LDL cholesterol, HDL cholesterol, triglycerides, or systolic or diastolic blood pressure. These findings persisted among the few study participants with one or more established risk factors at baseline. Conclusions: The occurrence of a heart attack or stroke in an immediate family member does not appear to lead to self-initiated, sustained change in modifiable risk factors in young adults. Since family history of heart attack and stroke is associated with known risk factors and is an independent risk factor for incident development of these conditions, interventions should be developed and tested to motivate sustained risk-factor control following occurrence of a severe vascular event in a family member. Copyright © 2002 American Journal of Preventive Medicine.