Tehran University of Medical Sciences Acta Medica Iranica 0044-6025 58 3 2020 07 19 126 129 Mehri Ayati Department of Pediatrics, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Amir Hossein Movahedian Department of Pediatrics, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. AND Department of Pediatrics, Bahrami Children’s Hospital, Tehran University of Medical Sciences, Tehran, Iran. Ziba Mosayebi Department of Pediatrics, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. AND Maternal, Fetal and Neonatal Research Center, Vali-Asr Hospital, Tehran University of Medical Sciences, Tehran, Iran. 2019 09 14 2020 04 25 Previous investigations have indicated an association between modulation of developing the immune system with increased risk of autoimmune diseases such as type 1 Diabetes Mellitus (T1DM). Objectives: In the present study, we aimed to evaluate correlations between the positive history of blood group incompatibility, neonatal jaundice, and phototherapy with childhood type 1 DM. A case-control retrospective study was carried out in an Iranian Hospital in 2015. One-hundred subjects aged 1-15 years with T1DM were included as the case group. One-hundred healthy children were also considered as the control group. A questionnaire composed of demographic-clinical data was completed for each subject. Correlations between childhood type 1diabetes and some clinical risk factors were determined. One hundred cases with type 1 diabetes and 100 healthy control children entered the study. A significant association between maternal gestational diabetes mellitus and childhood T1DM was observed (P=0.05, OR=3.789). The history of neonatal jaundice in the case group was significantly higher than in the control group (P=0.02, OR=4.667). ABO incompatibilities in the case group were associated with 19 neonates with blood group A and 2 neonates with blood group B (mothers' blood group; O) (P=0.005, OR=7.397). In the case group, 29 of 38 cases with a history of jaundice had received phototherapy while in the control group, 19 participants had undergone phototherapy (P=0.126, OR=1.707). Results have indicated that neonatal Jaundice and ABO incompatibility could increase the risk of childhood T1DM. Moreover, maternal GDM should be considered as an increased subsequent risk of childhood T1D. https://acta.tums.ac.ir/index.php/acta/article/view/8078 https://acta.tums.ac.ir/index.php/acta/article/download/8078/5383