OBJECTIVES: We evaluated an environmental intervention intended to increase sales of lower-fat foods in secondary school cafeterias. METHODS: Twenty secondary schools were randomly assigned to either an environmental intervention or a control group for a 2-year period. The intervention increased the availability of lower-fat foods and implemented student-based promotions. RESULTS: A steeper rate of increase in sales of lower-fat foods in year 1 (10% intervention vs -2.8% control, P =.002) and a higher percentage of sales of lower-fat foods in year 2 (33.6% intervention vs 22.1% control, P =.04) were observed. There were no significant changes in student self-reported food choices. CONCLUSIONS: School-based environmental interventions to increase availability and promotion of lower-fat foods can increase purchase of these foods among adolescents.