We used tree-structured survival analysis (TSSA), a computer-intensive method of classification, to determine prospectively the relation of the body mass index and the waist-to-calf circumference ratio to coronary heart disease and cancer mortality in 3,155 middle-aged men initially free of these diseases. Applied to coronary heart disease mortality, TSSA identified seven subgroups that differed in profile of risk factors and associated survival. Among the seven subgroups, a small subgroup of older, obese, normotensive men (N = 71) experienced an exceptionally high risk of coronary heart disease deaths over the 33 years of follow-up (34%), similar to the risk of 36% experienced by a larger subgroup (N = 387) of men of similar ages who were less obese and had higher blood pressure levels. We also observed a higher overall risk of coronary heart disease deaths during follow-up (10.3% vs 5.3%) in younger centrally obese men who had low blood pressure levels compared with their counterparts of similar age who were less obese. When applied to mortality from cancer of all sites, TSSA identified five subgroups that differed in survival distributions and profile of risk factors. A subgroup of younger, centrally obese, and ever-smoker men experienced a higher risk of cancer deaths than their counterparts who were less obese (14% vs 8%). Results from these analyses demonstrate the usefulness of a tree-structured analysis for classification of subjects into high- and low-risk survival subgroups.