The rapid increase of breast cancer in Taiwan has prompted the authors to evaluate the predictive factors of early menarche among contemporary Taiwanese girls. A total of 895 four-grade girls from eight elementary schools in Taipei City and County were identified as a closed cohort from the first semester of 1993. Data were collected from self-administered questionnaires and school records. A total of 799 girls who had not menstruated in the first year remained in the group through 1994. The effects of potential predictive factors were assessed by logistic regression. Among the 799 girls followed, 69 (8.6%) had first menstruation between the fourth and fifth grades. Height, weight, body mass index and maternal early onset of menarche were positively related to the onset of menarche within the preceding year. Energy consumption during exercise showed only moderate association after being adjusted for age and weight. Calorie intake from junk food was not associated with early menarche within the preceding year. Poor interpersonal family relationships and stressful life events also showed a moderate association with early menarche. The data obtained supported the hypothesis that height, weight, body mass index and maternal early menarche are positive predictive factors of early menarche. The effects of exercise and childhood stress are less prominent.