The objectives of this study were to determine the prevalence of dysmenorrhoea in Omani high schoolgirls, its impact and the treatment used. Methods: A cross-sectional survey was carried out in May 2010 on 404 girls from two public high schools in the Muscat region. Data were collected by self-administered questionnaire including information on demographics, prevalence of dysmenorrhoea, severity, its impact, and the treatment used. Results: Overall, 94% (n = 380) of the participants had dysmenorrhoea. It was mild in 27% (n = 104), moderate in 41% (n = 155), and severe in 32% (n = 121). Dysmenorrhoea was the cause of limited sports activities in 81%, decreased class concentration in 75%, restricted homework in 59%, school absenteeism in 45%, limited social activities in 25%, and decreased academic performance in 8% of the affected students. Only 3% (n = 10) had consulted a physician; 21% (n = 80) self-medicated, and 55% (n = 210) took no action. The commonest drugs used were paracetamol (n = 60, 16%), ibuprofen (n = 29, 8%) and mefenemic acid (n = 12, 3%). There was no statistically significant correlation between dysmenorrhoea, demographics and menstrual characteristics. Conclusion: Dysmenorrhoea is a prevalent and yet undertreated menstrual disorder among Omani adolescent schoolgirls. The pain suffered can be severe and disabling. Doctors should therefore be prepared to discuss this more freely with schoolgirls. In addition, there is a need for education regarding dysmenorrhoea and treatment options to minimise the impact on school, sports, social and daily activities.