Objective: Evaluate the relationship between low social support (SS) and adherence to diet in a cardiovascular disease (CVD) lifestyle intervention trial. Design: Prospective substudy. Setting and Participants: Blood relatives/cohabitants of hospitalized cardiac patients in a randomized controlled trial (n = 458; 66% female, 35% nonwhite, mean age 50 years). Main Outcome Measures: Non-adherence to diet using MEDFICTS (Meats, Eggs, Dairy, Fried foods, fat In baked goods, Convenience foods, fats added at the Table, and Snacks) tool; SS using the Enhancing Recovery in Coronary Heart Disease Patients Social Support Instrument. Analysis: Logistic regression models adjusted for confounders. Results: Significant predictors (P less than 0.05) of non-adherence to diet recommendations at 1 year included low SS, increased body mass index and waist size, lower physical activity, depression, pre-action stages of change, control group assignment, and being male. Those with low SS at baseline 2.7 greater odds of being non-adherent to diet at 1 year vs those with higher SS (95% confidence interval = 1.1 - 6.4); there was no interaction by group assignment. Conclusion and Implications: Low SS at baseline was independently associated with non-adherence to diet at 1 year, suggesting that family members with low SS may be at heightened CVD risk as a result of poor dietary adherence. (Contains 4 tables and 1 figure.)