Introduction: Premenstrual syndromes are among the disorders associated with reproductive age that includes physical, cognitive, emotional, and behavioral signs during the luteal phase that occurs periodically from 7 to 14 days before menstruation. These signs are not present at the begining of menstruation or during the first few days of bleeding. The aim of this study was to investigate the frequency of premenstrual syndromes in high school girls of Ilam during the year 2015.
 
Materials & Methods: This descriptive-analytic study has been performed on 266 single girl- students aged from 15 to 18 years, with the average age of 16.34, considered to have regular and natural menstruation cycles (with gaps of 21 to 35 days between each two menstruations lasting for 3 to 7 days). To assess the frequency of premenstrual syndromes, the prospective questionnaires (Premenstrual Symptoms Screening Tool: PSST) was used for two consecutive cycles. In this research, statistical tests such as Chi-square, Variance analysis, and Logistic regression were applied to analyze the data.
 
Findings: Based on our results, the frequency of medium or sever premenstrual syndromes was 36.84% and the frequency of premenstrual dysphoric disorder was 11.65%. According to logistic regression model, severe bleeding multiplies chances of the individuals suffering from dysphoric disorder by 5.1 times, while pain multiplies chances of the girls suffering from premenstrual syndrome about 4.1. There was a significant relation between the mild and severe premenstrual syndrome with pain, (P<0.001), and also between premenstrual dysphoric disorder and volume of bleeding (P<0.01). Investigating the mean for the 19 signs, the highest averages stood for fatigue, possession of physical signs, trouble or lack of concentration, reduction in interest of participation in normal routines, and anger; while the lowest average stood for over eating. 
 
Discussion & Conclusion: Our research concluded that prevalence of such syndromes among Ilami's high school girl-students was relatively high. Considering the negative effects of these syndromes on physical condition as well as psychological, emotional, and social wellbeing of teenagers, and the significance of this period from the educational point of view, more investigations and interventional moves are recommended to manage these signs.