There are few data available about the menstrual patterns of Australian teenagers and the prevalence of menstrual disorder in this age group. Aims To establish the typical experience of menstruation in a sample of 16-18 year old women attending ACT Secondary Colleges of Education. To determine the number of teenagers experiencing menstrual disorder that could require further investigation and management. Method The MDOT questionnaire was used to survey participants about their usual pattern of menstruation, signs and symptoms experienced with menses and how menstruation affected various aspects of their lives including school attendance, completion of school work, relationships, social, sexual and physical activity. Data analysis included exploration of aggregated data, as well as individual scrutiny of each questionnaire to determine menstrual disturbance requiring follow up. Those participants whose questionnaire indicated a requirement for further investigation, and who consented to being contacted, were followed up through an MDOT Clinic. Results One thousand and fifty one (1,05 1) completed questionnaires - 98% response rate. The typical experience of menstruation in the MDOT sample includes: bleeding patterns within normal parameters for this age group; menstrual pain, 94%; cramping pain, 71 %; symptoms associated with menstruation, 98.4%; PMS symptoms, 96%; mood disturbance before or during periods, 73%; school absence related to menstruation, 26%; high menstrual interference on one or more life activity, 55.8%; asymptomatic menstruation, 1 %; True response to 'My periods seem pretty normal' 7 1.4%. Statistically significant associations were found between each and all of: menstrual pain, symptoms, interference on life activities and school absence. The prevalence of significant menstrual disturbance in the sample is approximately 25% where: 2 1 % experienced severe pain; 26% reported school absence; 33% had seen a GP about periods; 26.9% think there is something wrong with periods; 23.5% require follow up based on individual scrutiny of each questionnaire; 10- 14% require further investigation to rule out endometriosis. Referral and investigation of menstrual pain, symptoms, and diagnosis of menstrual pathology in the sample was low. Conclusion The MDOT questionnaire has helped to establish a clearer picture of typical menstruation in the population sample. Where 1% of girls reported having asymptomatic menstruation, the majority of teenagers in the study reported menstrual pain and symptoms that could be experienced as part of the dysmenorrhoeic syndrome of symptoms, PMS, or underlying pathology such as endometriosis. Due to the overlap in symptoms and a propensity to be dismissive of menstrual pain and symptoms, many girls are suffering menstrual morbidities that could be well managed with NSAIDs and the oral contraceptive pill (OCP) if non-pathological, or investigated further if a menstrual pathology is suspected. Considering these results the reported school absence rate of 26% is not surprising. Whilst this study does not cost the true impact of menstrual disturbance on schooling, the results of the MDOT questionnaire reflect significant physical and emotional impact on a considerable number of teenager's lives which could also have repercussions on education, schooling performance and other areas of their lives. Future research is planned to determine the MDOT questionnaire's validity for identifying pathological menstrual disorder so it can act as a screening tool to facilitate earlier detection. Replication of the MDOT study should be done in younger teenagers (from menarche) to determine menstrual disturbance in the younger age group.