Pubertal development between 8 and 18 years is reported in 142 Swiss females of the First Zurich Longitudinal Study (1954-1980). Genital and pubic hair development were rated according to TANNER [9]. Pubertal development was initiated at the earliest between 8 and 9 years and at the latest between 14 and 15 years of age. The first secondary sex character in 53% of the girls was the onset of pubic hair development and in 18% the onset of breast development. In 29% both the initiation of breast and that of pubic hair development were observed as the first pubertal signs. Pubertal development was completed at the earliest between 12 and 13 years and at the latest between 17 and 18 years of age. Most pubertal stages of breast and pubic hair development tended to be reached at earlier ages than previously reported. Omissions of stages occurred only in a few percent of the girls. A notable exception was breast stage 4 which was absent in 33%. Reversions of stages, particularly of breast stage 5 to a lower breast stage, were occasionally observed. The mean duration of breast development was 3.2 +/- 1.4 years and pubic hair development 3.6 +/- 1.1 years. The mean age at menarche was 13.4 +/- 1.0 years. Menarche was reached on the average 2.2 years after the initiation of breast development and 2.7 years after the initiation of pubic hair development. In spite of large variations in timing and duration of pubertal stages some significant relationships were noted between the pubertal characters. Moderate correlations were found between the ages at initiation of breast and pubic hair development and menarche. The ages at completion of breast and pubic hair development, menarche and the age at which the peak of the adolescent growth spurt (PHV) was reached were highly correlated with each other. There was no significant relationship between the duration of breast development and that of pubic hair development. Furthermore, no clear relationship between the timing of pubertal development and its duration could be established. In contrast to previous reports the temporal relationship between pubertal development and the adolescent growth spurt was found to be similar in both sexes.