Objective: To determine whether effectiveness of a diet intervention for family members of cardiovascular disease patients varies by participant sex, race/ethnicity, or age because these characteristics have been associated with unique barriers to diet change. Design: Randomized controlled trial. Setting and Participants: University medical center. Healthy adult family members of patients hospitalized with cardiovascular disease (n = 501; 66% women; 36% racial/ethnic minorities; mean age 48 years). Intervention: A special screening and educational intervention (SI) vs control intervention (CI) to reduce dietary saturated fat and cholesterol intake throughout 1 year. Main Outcome Measures: Absolute change in MEDFICTS (meats, eggs, dairy, fried foods, fat in baked goods, convenience foods, fats added at the table and snacks) diet score, saturated fat, and dietary cholesterol in the SI vs CI from baseline to 1 year. Analysis: t tests stratified by sex, race/ethnicity, and age group; linear regression. Significance set at P less than 0.05. Results: The SI was effective to improve MEDFICTS score independent of sex, race/ethnicity, and age group (b = -6.7; P less than 0.001). There was no interaction between the SI and sex (b = 0.9; P = 0.84), race/ethnicity (b = -1.1; P = 0.81), or age group (b = -0.6; P = 0.89) on change in MEDFICTS score or change in saturated fat or dietary cholesterol intake from baseline to 1 year. Conclusions and Implications: Results support the potential for a hospital-based screening and education program to improve diet in diverse populations of cardiovascular disease patient family members. (Contains 4 tables.)