OBJECTIVE Puberty affects sleep phasing. However, it is unclear if sleep duration earlier in childhood could influence the timing of pubertal events. We aimed to assess the association between middle childhood nighttime sleep duration and age at menarche (AAM). METHODS In a cohort of 819 premenarcheal Colombian girls who were followed annually for the occurrence of menarche, we estimated adjusted hazard ratios (HR) with 95% confidence intervals (CI) for menarche by categories of recommended sleep duration in middle childhood using Cox models. Analyses were stratified by age at sleep assessment. RESULTS Among girls aged 9 to <11 years, compared with girls who slept within recommendations, sleeping above recommendations was related to an adjusted 76% (95% CI: 4%, 198%; p = .04) higher probability of experiencing menarche during follow up. In girls aged ≥11 years, compared with girls who slept within recommendations, sleeping under recommendations was related to an adjusted 42% (95% CI: 5%, 93%; p = .03) higher probability of experiencing menarche during follow-up. Sleep duration was not associated with AAM in girls aged <9 years at the time of sleep assessment. CONCLUSIONS Sleeping above recommendations in girls 9 to <11 years-old and sleeping under recommendations in girls ≥11 years-old is associated with earlier menarche.