The objective of the study was to determine if any anthropometric measurements, including weight, height, and upper arm circumference, or the calculated body mass index observed at the time of menarche may be used as a threshold for menarche. The sample was randomly selected from 1133 girls aged 10-18 years from two groups, one residing in Lima, Peru, at 150 m above sea level, and the second in Cerro de Pasco, Peru, at 4340 m above sea level. For the purpose of this study, all girls who reached menarche at least 1 month before the study (n = 93) were considered as cases (girls at menarche); 88 girls without menarche at the time of the study were randomly matched by age and place of residence, and designated as controls. All subjects came from the same low socioeconomic status. Body weight at menarche was 44.6 +/- 5.09 kg (mean +/- SD; coefficient of variation [CV], 11.4%). Height at menarche was 151.6 +/- 5.5 cm (CV, 3.7%). Body mass index, defined as weight/height2.15, was 18.26 +/- 1.96 kg/m2.15 at menarche (CV, 10.7%). Upper arm circumference at menarche was 21.8 +/- 1.6 cm (CV, 7.3%). The logistic regression analysis showed that any of the four anthropometric measurements analyzed were critical for menarche; i.e., any of the four could be used as a threshold for menarche. Data from the present study do not support the hypothesis that there are anthropometric markers that are critical for menarche.