en Epidemiology Epidemiology Original Research Original Research <p><strong>Background: </strong>Seasonality in suicide has been investigated from the early 19th century to explore the productive environmental variables.<br> Seasonality studies can provide information on prevention and interventions in suicide. In this study, we examined seasonality in<br> suicide and aimed to explore the differences in seasonality between rural and urban areas, mental disorders, and genders.<br> <strong>Methods:</strong> In this cross-sectional study, overall identified suicide cases in Ilam province from 21 March 2010 and 11 December 2014<br> were identified, using systematic registration suicide data (SRSD). Two methods were used separately to analyze seasonality (Chisquare,<br> Edwards&#39; T). Seasonal effect (peak/ trough seasons) and (deaths/ attempts suicide) was explored by ratio statistics. The null<br> hypothesis was that the completed suicides in each method group were evenly distributed over a year.<br> <strong>Results:</strong> Significant seasonality was observed in suicide during the study period, with one peak in the spring and one in the winter.<br> Our results showed that suicide seasonality following mental disorders was statistically significant with a peak in the spring, regardless<br> of other factors such as gender and age. When all non- mental suicides are taken into account, the seasonality remains statistically significant,<br> but the peak season is shifted to autumn.<br> <strong>Conclusion: </strong>Investigating suicide in Ilam revealed a significant seasonality for both rural and urban areas, which was greater in the<br> urban part. A significant seasonality in suicide was observed in attempters with mental disorders. In suicide attempters with mental<br> disorders, findings showed two peaks in the spring and the autumn.</p> Seasonality, Suicide, Mental disorders, Ilam, Iran 60 65 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-2533-2&slc_lang=en&sid=1 Yousef Veisani 200319475328460031199 200319475328460031199 No Psychosocial Injuries Research Center, Ilam University of Medical Sciences, Ilam, Iran. Ali Delpisheh alidelpisheh@yahoo.com 200319475328460031200 200319475328460031200 Yes Department of Clinical Epidemiology, Ilam University of Medical Sciences, Ilam, Iran. Kourosh Sayehmiri 200319475328460031201 200319475328460031201 No Social Medicine Department, Ilam University of Medical sciences, Ilam, Iran. Ghobad Moradi 200319475328460031202 200319475328460031202 No Social Determinants of Health Research Center, Kurdistan University of Medical Sciences, Sanandaj, Iran. Jafar Hassanzadeh 200319475328460031203 200319475328460031203 No Research Center for Health Sciences, Department of Epidemiology, School of Health, Shiraz University of Medical Sciences, Shiraz, Iran.