Background: It is thought that people with Down syndrome die younger than the general population, but that survival rates are improving. Methods: Five databases were searched for keywords related to intellectual disabilities, Down syndrome and mortality. Strict inclusion criteria were applied. Information from 34 selected studies was tabulated, extracted and synthesized. Results: People with Down syndrome died about 28 years younger than the general population. Congenital heart anomalies, comorbidities, low birthweight, and Black and minority ethnicity influenced earlier age of death, as did younger maternal age and poorer parental education. Congenital heart anomalies and respiratory conditions were the leading causes of death, and more common than in the general population. Survival rates have improved over time, particularly for those with congenital heart anomalies. Conclusions: People with Down syndrome are living longer but still die younger of different causes than the general population. More robust comparative data are needed, and ethnic differences require further study.