This paper describes the effectiveness of the Minnesota Heart Health Program (MHHP) in modifying mean body mass index (BMI) in whole communities. The MHHP is a 13-year research and demonstration project designed to reduce cardiovascular risk. One member of each of three pairs of matched communities received 7 years of community intervention activities that included risk factor screening, mass media education, adult education classes, worksite interventions, home correspondence programs, school-based programs, restaurant programs, and point-of-purchase education in supermarkets. Weight gain prevention was emphasized for all adults and weight loss was encouraged among those who were obese or who had elevated risk factors known to be responsive to weight loss (e.g., high blood pressure). A strong upward secular trend in weight was noted in all MHHP communities over time. Intervention effects were evaluated conservatively with community as the unit of analysis. This analysis showed no overall effect of the MHHP intervention program on mean BMI. However, a positive intervention effect was noted early in the intervention among those with elevated cholesterol or a history of obesity-related disease. Possible reasons for this relatively weak community effect are discussed, including secular forces overwhelming intervention effects, an intervention effort not sufficiently focused on obesity, ceiling effects for weight concern in a population that was highly aware of the issue at baseline, and inherent limitations in educational approaches for this recalcitrant public health problem.