Age at menarche varies with time of onset and the influence of social factors depends on the population under consideration. The objective of the present study was to determine the age at menarche among secondary school girls in Benin City, Nigeria and identify some of the social factors that might influence it. In this cross sectional study information on age at menarche was obtained from 1,640 menstruating secondary school girls (aged between 10 and 20 years) using the status quo method. Information sought in the structured questionnaire used included date of birth, date of menarche, educational attainment and occupation of parents, birth position, family size and State of origin. Data was analyzed using SPSS version 12.0. The mean age at menarche was 13.44±1.32 years (95% Confidence Interval, CI= 13.36-13.50). One out of every 15 (6.7%) girls below 12 years of age had attained menarche, indicating early menarche. There was statistically significant relationship between the mean menarcheal age and socioeconomic status (p< 0.001), birth position (p< 0.01) and family size (p< 0.01). The current mean age at menarche among secondary school girls in Benin City is 13.44±1.32 years and it is influenced by socioeconomic status, birth position and family size.