A cornerstone of treatment for hypercholesterolemia is dietary therapy. However, maintaining adherence to the therapeutic diet has been difficult for patients. There is evidence that self-efficacy is a predictor of positive behavior change like that involved in or necessary for initiating or maintaining recommended diet therapy for cholesterol reduction. This paper reports on two studies guided by Bandura's self-efficacy theory. The first study focuses on development and initial psychometric evaluation of an instrument measuring self-efficacy for adhering to a cholesterol-lowering diet in a sample of 44 cardiac rehabilitation patients; the second establishes psychometric properties of the instrument in a sample of 228 subjects treated for hypercholesterolemia. In both studies, subgroups completed the instrument a second time to provide data on the instrument's temporal stability. The Cholesterol-Lowering Diet Self-Efficacy Scale consists of 33 statements, some with branches for a total of 56 items. The scale measures several components of the eating habits domain related to adhering to a cholesterol-lowering eating plan, and shows good reliability and validity. Reported self-efficacy is related to prior persistence and past success in modifying and maintaining dietary changes, and also to concurrent measures of dietary adherence behaviors. The scale is psychometrically sound thus far and seems adequate in identifying success in achieving and maintaining a cholesterol-lowering eating plan.