The present study examines the characteristics of menstrual cycle among 361 Nigerian postmenarcheal schoolgirls derived from seven public secondary schools. Survey questions covered preparation for menstruation, duration of flow, cycle length, regularity, premenstrual syndrome and dysmenorrhea. For the study subjects the mean age (years) at the time of interview, at menarche, and completed since menarche are 16.5 +/- 3.3, 13.7 +/- 2.6 and 2.9 +/- 1.2 respectively. Premenstrual counselling was reported in 84.2%; and 48.6% was provided by parents and guardians, and 23.7% by school teachers. The findings indicate that menstrual flow < or = 2 days, and cycle length < or = 20 days are common; occurring in 20-30% of schoolgirls. Abnormal patterns such as cycle length > or = 38 days, flow duration > or = 8 days and heavy menstruation occurred in less than 5% of study subjects. Irregular menstrual cycles were recorded in 13%, and severe dysmenorrhea in 17.2%. Severe premenstrual syndrome occurred in about 20% of schoolgirls, with symptom-complex mainly of behavioural change, arousal and impaired concentration. The need for a multi-disciplinary school health counselling program that would provide relevant information on menstrual pattern and its common variation, identify abnormal patterns for early referral, provide psychological support and drug relief of distressing menstrual symptoms, and provide information on other contemporary adolescent problems is discussed.