In the feasibility study, children of both sexes, ages 8 to 10 at baseline starting in 1987, were randomized to either a control group or to a usual care group for whom more intensive dietary intervention for the child and the family was directed. The feasibility study lasted 16 months. The full-scale trial began in December 1988 with the randomization of a total of 663 children. At baseline, mean LDL-C levels, nutrient intakes, anthropometric measurements, nutritional biochemical levels, and psychosocial measures were similar in the two groups. The intervention group was assigned to a series of group and individual sessions to teach the children and their families to follow a diet containing 28 percent of calories as total fat, dietary cholesterol intake less than 75 mg/1000 kcal, and up to 9% of calories from polyunsaturated fat. The diets were designed to meet nutritional requirements of growing children. The usual care group was provided a packet of general dietary information only. The primary efficacy outcome was a difference in changes in LDL-C levels between the two groups at 36 months. Primary safety endpoints were change in height and serum ferritin levels. Secondary safety outcomes included serum zinc, retinol, albumin levels, red blood cell folate, ratio of LDL-C to high-density lipoprotein cholesterol, sexual maturation, cognitive development, and psychosocial assessments. Recruitment was completed in July 1990. Intervention and follow-up was extended until 1997 when the participants were on average 17 years old. Data analysis continued through January 1999.