The age at menarche and several menstrual symptoms were reported by 516 Portuguese school girls who took part in a cross-sectional anthropometric study in Coimbra, Portugal. The mean ages of menarche calculated using the recall method and also using probit analysis were 12.53 +/-1.27 and 12.03 +/- 1.26 years, respectively. Parents'educational level, place of residence and size of the family did not have any significant effect on the mean age at menarche in this sample of adolescents. The order of birth was the only variable that indicated a significative effect: the first borns reported a lower mean age at menarche (12.34 years) than the later borns (12.6 years). In this sample, 47% of the girls had a cycle length of >or = 29 days, 23.4% had irregular cycles, 59% reported that the duration of bleeding was 3-5 days and the majority, 49%, did not report any pain during the bleeding days. However, 14.3% and 24.45% reported severe and medium pain. The age at menarche has declined from 15.0 (girls born in 1880-1890) to 12.03 (girls born in 1970-1980) years in the Portuguese population. This decrease in age, and also the lack of influence of the family characteristics, appear as a result of the great improvements in the social and economic living conditions that occurred in Portugal, especially after the 1970s. These improvements are mainly related to better nutrition and better health care along with many other environmental factors.