This study evaluates the effectiveness of an intervention based on the concept of implementation intentions for reducing dietary fat intake. Participants (n=264) completed questionnaires on their motivation to eat a low-fat diet before being randomized to either an experimental condition, which required them to form an implementation intention, or a control condition. Results showed that, after 1 month, fat intake, saturated fat intake, and the proportion of energy derived from fat decreased significantly in the experimental group but not in the control group. This difference could not be explained by differences in motivation between the 2 groups. The findings are discussed in relation to the use of implementation intentions instead of tailored interventions to change behavior in general populations.