More than 800 15 year old members of the Dunedin Multidisciplinary Health and Development study cohort completed a questionnaire designed to provide descriptive data concerning the weight control behaviours of this sample of New Zealand adolescents. The results showed that approximately 75% of the adolescents were within acceptable body mass index ranges. However 68% of the girls (but only 19% of the boys) wanted to weigh less than their present weight. Generally, girls were more concerned about their body weight than boys: 26% of girls weighed themselves fortnightly or more often, compared with 12% of boys; 45% of girls reported that they were trying to lose weight at present, compared with 9.5% of boys. The main methods of weight reduction included weight reduction diets (21% of girls, 4% of boys in the previous year); exercise such as jogging, walking, swimming and cycling (60% of girls, 34% of boys); and participation in dieting and fitness clubs (35% of girls, 16% of boys). In addition, 20% of girls reported using techniques such as slimming tablets (3%), cigarette smoking (5%) and self-induced vomiting (5%) to control weight. The results show that weight control is a major preoccupation of many girls and some boys. Results are discussed in relation to differential social influences on the sexes, and health consequences.