This research was aimed at studying the stress, anxiety, and depression epidemiology among highschoolers in Mashhad, Iran. The sample included 605 students (341 males & 264 females) coming from various grades of high school ranging in age from 14 to 19. To fulfill the objectives of the study, three instruments (scales) were employed including the Perceived Stress Scale (PSS), Cattell Anxiety Scale (CAS), and Children Depression Scale (CDS-A). Since the PSS and CDS-A had no norm in Iran, they were then normed revealing reliability of 0.76 for PSS through Spearmen-Brown split half while it was 0.77 through Cronbach’s alpha. Similarly, the reliability for CDS-A was 0.9 and 0.89, respectively. In addition, the validity of the tests proved to be significant at p<0.001 once the correlation of each item with the whole test was obtained. Besides, factor analysis was conducted and examining the items which had the highest loadings on each item indicated that the items of the two tests were completely reliable. The epidemiology results indicated that the stress prevalence was 9.1% among the boys and 22% among the girls while it was 14.7% in the whole sample. This implies that the EBtela rate in girls was two and half times greater that the boys.