The pubertal development of 212 randomly selected Swedish urban children has been investigated as part of a prospective longitudinal study of growth and development. The timing and pattern of pubertal changes were in agreement with the findings in other contemporary studies. The good agreement with data on pubertal development reported in other investigations of Swedish children indicates that the present sample was representative of contemporary Swedish children. Two procedures of assessment of secondary sex characters - clinical examination and whole-body photography - have been compared and contrasted. A clinical examination is less laborious and resource-consuming and also has psychological advantages but should be supplemented in boys by the estimation of testicular volume (orchidometry). In girls the two methods have similar precision and reliability. The first pubertal changes may be observed before 9 years in girls (breast development) and before 10 years in boys (genital development). On average the first change takes place about one year earlier in girls than in boys. Peak height velocity (PHV) is an early event during puberty in girls and a relatively late event during puberty in girls and a relatively late one in boys, the sex difference in mean age being about two years. In girls, menarche is a late event, always occurring after PHV. At the age of 13-14 years some boys and girls have not yet begun theri pubertal development, while others have reached the adult stage.