The first U.S. population-based cancer prevention research unit identifies and tests primary prevention interventions that work at a community level. It selects the most common cancer sites and high impact, safe interventions, including the prevention and control of the use of tobacco and the identification of efficacious dietary interventions. A multidisciplinary team of investigators conceptualize, design, and implement interdisciplinary research projects within the framework of an over-all research plan. The interdisciplinary approach and the appropriateness of each project is assured by six core research resources which analyze enrollee and provider information from a large comprehensive health plan, monitor cancer registrations and health behaviors, facilitate general population and community-wide intervention strategies, provide expertise and tools for cost analysis, provide behavioral intervention expertise and tools, and provide tools for dietary measurements, nutrient databases, and short-term measurements of dietary effects. Current research projects include multicenter randomized chemoprevention trials, randomized community trials of smoking cessation and the prevention of tobacco use, community-based dietary change interventions, studies of the efficacy of a low-fat diet and of the diffusion and permanence of successful changes in fat consumption, and community-based intervention studies to increase rates of regular use of mammography.