Assessing a combination of modifiable lifestyle practices may be a practical tool to modify patients' health behavior in counseling. Therefore, we developed a chronic disease risk index (CDRI) and investigated its relation with chronic disease in a multiethnic cohort. A total of 15,693 men and 16,007 women in Hawaii who reported their diet and other lifestyle behaviors between 1975 and 1980 were followed until 1994. A semi-quantitative composite CDRI with scores ranging from 1 to 10 included the rankings for smoking, alcohol use, body mass index, fat intake, and fruit and vegetable consumption. Cox's proportional hazards regression was used to estimate the relative risk for chronic diseases. When comparing the highest to the lowest CDRI category, the respective relative risks (RRs) for total mortality were 2.9 (95% CI 2.3-3.8) and 3.8 (95% CI 2.9-5.0) for men and women. With higher CDRIs, the RRs for cancer incidence, mortality from cancer, coronary heart disease, and stroke increased significantly. Among the five components of the CDRI, smoking had the greatest influence on chronic disease risk, followed by body mass index. Positive health behavior reflected by the CDRI is associated with a lower risk of cancer and with greater longevity.