The authors carried out a population-based case-control study to estimate the risk of an acute coronary disease event associated with various definitions of a family history of coronary heart disease (CHD). A detailed family history questionnaire was completed by 403 cases and 236 controls in Newcastle, New South Wales, Australia from 1992 to 1994. Odds ratios of an acute coronary disease event adjusted for proband age and sex ranged from 2.7 (95% confidence interval (Cl) 1.8–4.1) for the simplest definition (one or more first-degree relatives with CHD at any age) to 5.4 (95% Cl 1.7–16.8) for the most stringent definition (two or more first-degree relatives with CHD before age 55 years). In a series of nested models, the authors examined the improvement in model fit as each component of the detailed family history was added. Additional information was provided by accounting for “don't know” responses, the number of affected relatives, the age of the affected relative, and whether the first-degree relative was a sibling rather than a parent. The results were similar when the data were analyzed as a cohort design with proband disease status as the exposure variable. The authors suggest that, to facilitate preventive efforts in a population, more detailed family history definitions should be used to better target high risk subjects. Am J Epidemiol 1998; 147: 1133–9.