There is some evidence for a decreasing age of menarche in many populations. This study examined the secular trend of age at menarche among Iranian women. Age at menarche based on recall information was recorded for 770 pairs of mother and daughters. Between 1930 and 1990 mean menarcheal age of this cohort of women decreased from 13.88 to 12.98 years (-0.15 years per decade) and mean height of the cohort increased from 152.33 to 158.43 cm (+0.99 cm per decade). There was a significant correlation between menarcheal age of mothers and their daughters (r = 0.27). Year of birth, mother's menarcheal age and daughter's height were significant predictors of daughter's menarcheal age.