BACKGROUND: Menarche is an important phase of female reproductive life, which with passage of time is getting earlier worldwide. Early menarche has several psychosocial and behavioral effects on a girl's teenage life, besides it increases the risk of breast cancer, therefore it is important to determine the underlying causes of this change. OBJECTIVE: To assess the extent of and factors responsible for variation in age at menarche in females of Sindh. STUDY DESIGN: Cross-sectional, questionnaire based. METHODOLOGY: The study was conducted by department of physiology on 600 sexually healthy females, belongs to interior Sindh, Hyderabad and Karachi. Informed written consent was obtained, data about menarcheal age and relevant factor was collected using questionnaires containing close-ended questions. Volunteers were divided into three groups, each of 200, based upon their birth year, Group 1 included ladies who were born in 1970s or before, Group 2 consists those who born in 1980s while volunteer from Group 3 were the youngest generation born during 1990's and onwards. RESULTS: Mean age at menarche for Group 1 was 13.6 yrs (Std. Dev ± 1.3), Group 2, 13.3 yrs (Std. Dev ± 1.0) and for Group 3 it was 12.3 yrs (Std. Dev ± 1.1). Pearson Correlation between age at menarche and menarcheal age of sister for all three groups was significant (P = 0.01). Twenty-three percent volunteers in Group 1, 37% in Group 2 (P = 0.01) and 48% in Group 3 (P = 0.02) had awareness about menstruation at their time of menarche. CONCLUSION: Menarcheal age, over time is decreasing, among girls of Sindh, Pakistan. This may be due to pre-menarcheal awareness and hereditary influence.