en غدد Endocrinology Research Article Research Article <div style="text-align: justify;"><strong>Background</strong>: The seasonality of type 1 diabetes and diabetic ketoacidosis at diagnosis have been reported in most areas of the world, but there are few reports from north of Iran.<br> <strong>Objectives</strong>: Considering the connection between type 1 diabetes mellitus (T1DM) diagnosis and environmental influences, this study aimed to evaluate the seasonal trends of T1DM and diabetic ketoacidosis (DKA) at the time of diagnosis over a 10-year period.<br> <strong>Methods</strong>: In a retrospective study spanning two 5-year periods, 221 pediatric patients with T1DM were analyzed. They were categorized into two groups: Group 1 comprised those diagnosed from 2011 to 2015, while group 2 consisted of patients diagnosed from 2016 to 2020 (pre-COVID-19 quarantine). Changes in type 1 diabetes onset and DKA at diagnosis were assessed using Mann&ndash;Kendall trend test. Monthly and seasonal variation of type 1 diabetes and DKA at diagnosis were assessed over a 10-year period comparing two 5-year intervals. The data were analyzed using STATA software, version 17. &nbsp; &nbsp;<br> <strong>Results</strong>: Of the 221 individuals, 101(45.7%) and 120(54.3%) patients were diagnosed in group 1 and 2, respectively. The Mann&ndash;Kendall trend test revealed significant changes in both T1DM onset and DKA at diagnosis over the period 2011&ndash;2020 (tau=0.6138, P=0.0191) and (tau=0.582, P=0.0287), respectively. The increase in T1DM onset occurred in spring and June during the second period. The mean age at diagnosis was 7.2&plusmn;4 years, with group 1 (6.63, 95% CI, 5.75%, 7.51%) being younger than group 2 (7.58, 95% CI, 6.83%, 8.33%). The frequency of adolescent patients significantly increased in the group 2 compared to group 1 (71.2% vs 28.8%, P=0.04). In both periods, there was a predominance of female sex, and the seasonal pattern of female sex shifted towards spring and summer in group 2. The frequency of DKA at presentation was 37.1% (95% CI, 30.9%, 43.7%) over a ten-year period, with 32.7% (95% CI, 24.2%, 42.4%) in group 1 and 41% (95% CI, 32.4%, 50%) in group 2 (P=0.35). An analysis of the seasonal pattern of initial presentations with DKA indicates that group 1 patients exhibited the highest rate of DKA in the summer and autumn, with the lowest rate in the spring. Meanwhile, group 2 patients displayed that DKA at diagnosis was highest in summer and lowest in autumn.<br> <strong>Conclusions</strong>: The onset of T1DM and DKA shows a shift toward warmer seasons.</div> Seasonal variation, Type 1 diabetes, Children, Diabetic ketoacidosis (DKA), Epidemiology 163 176 http://jpr.mazums.ac.ir/browse.php?a_code=A-10-1073-4&slc_lang=en&sid=1 Mobin Ghazaiean dr.mobin.gh@gmail.com 100319475328460013777 100319475328460013777 No Student Research Committee, Faculty of Medicine, Mazandaran University of Medical Sciences, Sari, Iran. Behnam Najafi behnam.najafi.185@gmail.com 100319475328460013778 100319475328460013778 No Student Research Committee, Faculty of Medicine, Mazandaran University of Medical Sciences, Sari, Iran. Daniel Zamanfar danielzamanfar@yahoo.com, daniel.zamanfar2024@gmail.com 100319475328460013779 100319475328460013779 Yes Diabetes Research Center of Mazandaran, Mazandaran University of Medical Sciences, Sari, Iran.