The increasing prevalence of overweight and obesity among female adolescents is a global health problem. In developing countries such as South Africa, this increase is often associated with urbanisation and the adoption of a Western lifestyle. Two aspects of the Western lifestyle that contribute to the development of overweight and obesity are a decrease in physical activity levels and an increase in the consumption of energy-dense food, high in fats and refined sugar. Information on the prevalence of increased body fatness in populations in transition is scarce, but necessary for effective planning and intervention. Current indications are that there is a trend towards unhealthy behaviour among high-school girls, globally and in South Africa. Schools can play an important role in the prevention of overweight and obesity among schoolgirls. It is recommended that school governing bodies institute remedial action to prevent weight gain in children, especially girls.