Surveillance of age at menarche could provide useful information on the impact of changing environmental conditions on child health. Nevertheless, nationally representative data are exceedingly rare. The aim of this study was to examine trends and sociodemographic correlates of age at menarche of Colombian girls. The study sample included 15,441 girls born between 1992 and 2000 who participated in the Colombian National Nutrition Survey of 2010. We estimated median menarcheal age using Kaplan–Meier time-to-event analyses. Hazard ratios with 95% confidence intervals were estimated with Cox regression models. The median age at menarche was 12.6 years. There was an estimated decline of 0.54 years/decade (P < 0.001) over the birth years; this decline was only observed among girls from urban areas, and was more pronounced among girls from wealthier versus poorer families. Child height and BMI, maternal BMI and education, and family wealth were each inversely associated with menarcheal age whereas food insecurity and number of children in the household were positively associated with age at menarche. In conclusion, a negative trend in age at menarche is ongoing in Colombia, especially in groups most likely to benefit from socioeconomic development.