Background: Early onset of menarche is considered an important risk factor for a number of diseases in adulthood. Iron intake may be related to pubertal timing because of its role in childhood growth and reproductive function. Objective: We investigated the relation between dietary iron intake and age at menarche in a prospective cohort of Chilean girls. Methods: Overall, 602 Chilean girls were included in the Growth and Obesity Cohort Study, a longitudinal study that began in 2006 when the girls were 3–4 y old. Starting in 2013, diet was assessed every 6 mo through 24-h recall. The date of menarche was reported every 6 mo. Our analysis included 435 girls with prospective data on diet and age at menarche. We used a multivariable Cox proportional hazards regression model with restricted cubic splines to estimate HRs and 95% CIs for the association between cumulative mean iron intake and age at menarche. Results: Most girls (99.5%) attained menarche with a mean (standard deviation) age at menarche of 12.2 (0.9) y. The mean dietary iron intake was 13.5 (range: 4.0–30.6) mg/d. Only 3.7% of girls consumed below 8 mg/d, the RDA. After multivariable adjustment, cumulative mean iron intake had a nonlinear association with menarche (P-for-nonlinearity: 0.02). Iron intakes above the RDA, between 8 and 15 mg/d, were associated with progressively lower probability of earlier menarche. Above 15 mg/d, the HRs were imprecise but tended to approach the null as iron intake increased. This association was attenuated after adjusting for girls’ BMI and height before menarche (P-for-nonlinearity: 0.11). Conclusion: In Chilean girls, iron intake during late childhood, independent of body weight, was not an important determinant of menarche timing.