Less than 50% of US adults follow dietary recommendations. Despite these figures, little research has focused on improving adherence to a therapeutic eating plan. The research utilizing self-efficacy theory has shown promise for improving behavior change and treatment adherence. This study evaluated the efficacy of a telephone-delivered, self-efficacy based intervention designed to improve adherence to a cholesterol-lowering diet among those self-reporting nonadherence. Sixty-five men and women diagnosed with hypercholesterolemia were randomized to usual care or treatment, which consisted of six intervention sessions delivered every 2 weeks by telephone and focused on how to manage eating behavior in challenging situations. There were significant between group differences post intervention in the consumption of saturated fat (P < .001) and cholesterol (P = .040) with the intervention group improving their dietary adherence. Significant change (P = .013) occurred over time in low-density lipoprotein-cholesterol (LDL-C) in the intervention group. No changes were observed in self-efficacy between groups, suggesting that self-efficacy was not a mediator of the improved adherence. The study's findings confirm that the telephone is a useful tool to deliver adherence-enhancing interventions.