Background Age at menarche is a significant indicator of growth and sexual maturation in girls. During adolescence, anthropometry provides a tool for monitoring and evaluating the hormone-mediated changes in growth and reproductive maturation. Objectives We aimed to examine the anthropometric status of pre- and post-menarcheal Nigerian adolescent girls attending senior secondary schools. Materials and Methods In this school-based cross-sectional survey, a pre-tested structured self-administered questionnaire was set for obtaining the socio-demographic data (age at menarche, number of siblings, occupation and educational attainment of their parents, etc.), while the anthropometric status data was obtained by direct measurement of weight and height. The body mass index (BMI) and the ponderal index (PI) of each participant were computed from their respective weight and height values. The study was designed to include all the students in the two schools that were randomly selected. The anthropometric indices of pre- and post-menarcheal girls were compared. Results Out of a total population of 2,166 students, 2,159 (99.7%) participated but 9 questionnaires were incompletely filled and were rejected, leaving 2,150 (510 were pre-menarcheal and 1,640 were post- menarcheal) for further analysis. The mean menarcheal age was 13.44 ± 1.32 years (95% Confidence Interval (CI) = 13.38-13.5). Girls from families with high socio-economic status (SES) attained menarche 8.0 and 9.0 months earlier than their counterparts from families with middle and low SES respectively. Girls from small-size families had a significantly lower menarcheal age than their counterparts from large-size families. A comparison of the anthropometric indices of pre- and post-menarcheal girls showed: weight, 41.1 ± 6.3 kg (95% CI = 40.6-41.6) vs 47.6 ± 7.2 kg (95% CI = 47.3-47.9), P < 0.001; height, 146.2± 5.5 cm (95% CI = 145.7-146.7) vs 153.6 ± 9.9 cm (95% CI = 153.1-154.1), P < 0.001; BMI, 16.4 ± 1.9 (95% CI = 16.2-16.6) vs 18.8 ± 1.6 (95% CI = 18.7-18.9), P < 0.001; and PI, 45.1 ± 1.7 (95% CI = 45.0-45.2) vs 44.6 ± 1.4 (95% CI = 44.5-44.7), P < 0.01. Conclusions Post-menarcheal girls were significantly taller and heavier with a higher BMI than their pre-menarcheal counterparts, but the pre-menarcheal girls possessed a better linear body as reflected by the PI.