INTRODUCTION: Migrant women often experience worse perinatal outcomes during pregnancy, birth, and puerperium than native women, but results regarding preterm birth vary. The objective of this study was to detect the prevalence and risk factors of preterm birth among Icelandic and migrant women in Iceland. MATERIAL AND METHODS: The study was a population-based cohort study with data from the Icelandic Medical Birth Register. The cohort included all women who had a singleton birth from 22w0d to 36w6d of pregnancy in the years 1997-2018, a total of 89 170 women. The group was divided in two; women with an Icelandic citizenship and women with foreign citizenship, that were further divided according to the Human Development Index (HDI) of their country of citizenship. Preterm birth rate and risk factor prevalence was analysed according to this classification and significance in differences measured with a chi-square test. RESULTS: Significance in differences of preterm birth was found between Icelandic (4.4%) and migrant women (5.6%) (p<0.001). Migrant women from middle-HDI countries gave birth preterm in 5.5% of cases (p<0.01) and women from low-HDI countries in 6.4% of cases (p<0.001). Migrant women were more often diagnosed with urinary tract infections, diabetes, intrauterine growth restriction and premature rupture of membranes, but less often with pre-eclampsia, obesity, placental defect, mental health issues and age <18 years (p<0.05). CONCLUSION: Migrant women in Iceland from middle-HDI and low-HDI countries give birth preterm more often than Icelandic women. A difference in risk factors is also present and needs further research. The findings can be used in continuing development of prenatal care for migrant women in Iceland.