Recent studies of vegetarian diets and their effects on morbidity and mortality are reviewed. Vegetarian diets are heterogeneous as are their effects on nutritional status, health, and longevity. Mortality rates are similar or lower for vegetarians than for nonvegetarians. Risks of dietary deficiency disease are increased on vegan but not on all vegetarian diets. Evidence for decreased risks for certain chronic degenerative diseases varies. Both vegetarian dietary and lifestyle practices are involved. Data are strong that vegetarians are at lesser risk for obesity, atonic constipation, lung cancer, and alcoholism. Evidence is good that risks for hypertension, coronary artery disease, type II diabetes, and gallstones are lower. Data are only fair to poor that risks of breast cancer, diverticular disease of the colon, colonic cancer, calcium kidney stones, osteoporosis, dental erosion, and dental caries are lower among vegetarians. Reduced risks for chronic degenerative diseases can also be achieved by manipulations of omnivorous diets and lifestyles.