Age at menarche in girls born from 1985 to 1989 in Mazandaran, Islamic Republic of Iran.

This cross-sectional study was carried out on 2246 girls born between 1985 and 1989 to determine the age of menarche in Mazandaran province, northern Islamic Republic of Iran. Six cities were selected randomly and cluster sampling used to select high-school students in urban and rural areas. Students with malnutrition, anaemia and chronic infections such as tuberculosis were excluded. The mean (standard deviation) age of menarche was 12.5 (1.1) years, 95% CI: 12.45-12.55 years. The most frequent occurrence of menarche was in summer and least frequent in winter. Menarche age was significantly higher in girls living in rural areas and with fathers with lower education.