Background International migration has increased during the past years and little is known about the mortality of young adult immigrants and refugees that came to Sweden as children. This study aimed to investigate 1) the risk of all-cause and cause-specific mortality in young accompanied and unaccompanied refugees and non-refugee immigrants compared to Swedish born individuals; and 2) to determine the role of educational level and migrations-related factors in these associations. Methods This register linkage study is based on 682,358 individuals (633,167 Swedish-born, 2,163 unaccompanied and 25,658 accompanied refugees and 21,370 non-refugee immigrants) 19-25 years old, who resided in Sweden 31.12.2004. Outcomes were all-cause mortality and mortality due to suicide and external causes. Hazard ratios (HR) and 95% confidence intervals (CI) were calculated using Cox regression models with a maximum follow-up to 2016. Results After adjusting for covariates, all-cause mortality was significantly lower in non-refugee immigrants (aHR 0.70, 95% CI 0.59-0.84) and refugees (aHR 0.76, 95% CI 0.65-0.88) compared to Swedish-born individuals. The same direction of association was observed for mortality due to suicide and external causes. No differences between accompanied and unaccompanied refugees were found. Risk estimates for all migrant groups varied with educational level, duration of residency, age at arrival and country of birth. Further, the mortality risk of migrants arriving in Sweden before the age of 6 years did not significantly differ from the risk of their Swedish-born peers. Low education was a considerable risk factor. Conclusion In general, young adult refugees and non-refugee immigrants have a lower risk of all-cause and cause-specific mortality than Swedish-born individuals. The identified migrant groups with higher mortality risk need specific attention.