This study seeks to further elucidate the mother-daughter hormonal relationship and its effects on daughter's breast cancer risk through the association with early age at menarche. Four hundred and thirty-eight healthy girls, age 9-18 and of White, Asian, and/or Polynesian race/ethnicity, were recruited from an HMO on Oahu, Hawaii. Anthropometric measures were taken at a clinic visit, and family background questionnaires were completed. Cox proportional hazards regression was used to test the association of maternal and intrauterine hormone-related exposures with age at menarche. Weight and gestational age at birth and maternal pregnancy-induced nausea were not associated with age at menarche. Each year older of the mother's age at menarche was associated with a 21% reduced risk of an early age at menarche for the daughter (95% CI: 0.73-0.86). This association between mother's and daughter's menarcheal age was statistically significant for girls of Asian, White, and Mixed, Asian/White race/ethnicity, but not for girls of Mixed, part-Polynesian race/ethnicity (p (interaction) = 0.01). There was a suggestion that maternal history of breast cancer was associated with an increased risk of early age at menarche (HR = 2.18, 95% CI: 0.95-4.98); there was no association with second-degree family history. These findings support the hypothesis that maternal and intrauterine hormone-related exposures are associated with age at menarche.