This study aimed to assess the timing of sexual maturation (breast development and menarche occurrence) among sub-Saharan African adolescent girls from rural areas. In the framework of a longitudinal study of growth at puberty, the stages of pubertal development (Tanner classification) and menarche occurrence were recorded at intervals between 1995 and 2000 in a sample of 406 Senegalese adolescent girls from a rural area. Nutritional status was estimated during infancy, childhood, and adolescence within this sample, and body composition was estimated only during adolescence. At the beginning of the study (1995), the adolescent girls were 11.4 years old (SD = 0.6). At the end of the study, they were 16.5 years old (SD = 0.6). Median and quartile ages at entry into each maturity stage and its confidence limits were estimated by a lognormal parametric survival model. These adolescent girls were shorter and thinner than girls of the same age from developed countries. Median age at the onset of breast development was 12.6 years (95% CI = 12.5-12.8). Median age at the end of sexual maturation and median age at menarche were estimated respectively at 15.8 years (95% CI = 15.7-15.9) and 15.9 years (95% CI = 15.7-15.9). These adolescent girls were less mature than other adolescent girls of the same age from other developing countries. Their puberty was extremely delayed compared to that of adolescent girls of the same age from industrialized countries. Puberty in these Senegalese adolescent girls is delayed by about 3 years. This may be due to malnutrition, significant energy expenditure, and poor diet and living conditions, and possibly to genetic control.