The objective was to analyze the relationship between socioeconomic status and age at menarche among indigenous and non-indigenous girls in the Araucanía Region of Chile, controlling for nutritional status and mother's age at menarche. A total of 8,624 randomly selected girls from 168 schools were screened, resulting in the selection of 207 indigenous and 200 non-indigenous girls who had recently experienced menarche. Age at menarche was 149.6±10.7 months in the indigenous group and 146.6±10.8 months in the non-indigenous group. Among the non-indigenous, the analysis showed no significant association between age at menarche and socioeconomic status. In the indigenous group, age at menarche among girls with low socioeconomic status was 5.4 months later than among those with higher socioeconomic status. There were no differences in nutritional status according to socioeconomic level. Obesity was associated with earlier menarche. Menarche occurred earlier than in previous generations. An inverse relationship between socioeconomic status and age at menarche was seen in the indigenous group only; low socioeconomic status was associated with delayed menarche, regardless of nutritional status or mother's age at menarche.