Data are presented from the first four groups studied in a longrange investigation of human ecology in the Solomon Islands. The groups varied in habitat, way of life, genetic background, and exposure to Western influence. Coverage of residents in designated hamlets was 78% for Kwaio, Malaita Island; 91% for Nasioi, Bougainville Island; and over 95% for both Lau and Baegu of Malaita. In all, 1626 persons were studied: 256 Nasioi, 443 Kwaio, 442 Lau, and 485 Baegu. All four groups were demographically “young,” with a high ratio of persons under 15 to those over 45 years of age, but a significant proportion lived to old age. Nutrition was adequate, though low in protein and fat. They had very little color-blindness and virtually no myopia, astigmatism, glaucoma, or hypertensive and coronary heart disease. Malaria, trachoma, and intestinal parasitism reflected differences in habitat and ways of life, but tuberculosis did not. Despite a density as high as that recorded for any human population, the Lau, living on small artificial islets in a saltwater lagoon, enjoyed robust health.