Body size, composition, and conformation in a teen-age population, and associated factors were studied to obtain useful data for planning programs in public health nutrition. This book describes the purpose, methods, and findings of this four-year longitudinal and cross-sectional study conducted in Berkeley, California, during the years 1961 to 1965. Subjects numbered roughly 1,000 teenagers each year, studied at successive grade levels from nine through twelve. Body composition and conformation were assessed annually for the entire sample, as were subjects' views regarding body size and shape, food, and activity. Definitive studies of body composition, food intake, and activity were conducted with a subsample of approximately 200 subjects. Eight aims of the study were: (1) to determine anthropometric measurements over a four-year period; (2) to obtain a measure of food intake and physical activity to determine possible associations between these and composition, conformation, sex, age, race, and socioeconomic status; (3) to utilize the body measurement data to substantiate a set of principles regarding composition, conformation, and growth; (4) to determine the prevalence of obesity, the time of onset, and, if possible, the relative effects of food intake and physical activity on its occurance; (5) to determine associations between body measurements and performance as indicated by standardized physical performance tests, school attendance, and grades; (6) to test the feasibility of the study's methodology in a public school setting; (7) to validate the accuracy of the methodology; and (8) to learn something of the teenagers' attitudes toward body size, food intake, and physical activity. Statistical data, regression equations, forms used in the study, and case histories are appended. (MM)