Mental disorders are importance disorders in young adults. The present study aimed to investigate the prevalence of depression and its relationship with decline of students´ educational performance among high school students. In a correlation study, the study population was consisted of all high school students enrolled in the academic year 2008-2009 in Ilam, Iran. A multi-stage sampling method was used. Data were collected by both demographic and Beck Depression Inventory questionnaires. The student's educational performance was evaluated from extracted on the first and second semester’s average score. A decline of students’ educational performance was considered if the student's semesters average score was lower in second semester in compared to the first semester. Totally, 25.7 % of the students have mental health. The depression distribution was 32.2% in mild mood disturbance, 14.6% in borderline clinical depression, 17.1% in moderate depression, 8.5% in severe depression and 2% extreme depression. Overall, 57.3% of students were experiencing a decline of students’ educational performance. There was a statistically significant relationship between depression and a decline of students´ educational performance. The lower the parent education was associated with the higher decline of students’ educational performance. Depression remains a serious problem. Identify risk factors for depression disorder is necessary in order to promote health and students´ educational performance
