Background: European societies are rapidly ageing and becoming multicultural. We studied differences in overall and cause-specific mortality between migrants and non-migrants in Belgium specifically focusing on the older population. Methods: We performed a mortality follow-up until 2009 of the population aged 50 and over living in Flanders and the Brussels-Capital Region by linking the 2001 census data with the population and mortality registers. Overall mortality differences were analysed via directly age-standardized mortality rates. Cause-specific mortality differences between non-migrants and various western and non-western migrant groups were analysed using Poisson regression models, controlling for age (model 1) and additionally controlling for socio-economic status and urban typology (model 2). Results: At older ages, most migrants had an overall mortality advantage relative to non-migrants, regardless of a lower socio-economic status. Specific migrant groups (e.g. Turkish migrants, French and eastern European male migrants and German female migrants) had an overall mortality disadvantage, which was, at least partially, attributable to a lower socio-economic status. Despite the general overall mortality advantage, migrants experienced higher mortality from infectious diseases, diabetes-related causes, respiratory diseases (western migrants), cardiovascular diseases (non-western female migrants) and lung cancer (western female migrants). Conclusion: Mortality differences between older migrants and non-migrants depend on cause of death, age, sex, migrant origin and socio-economic status. These differences can be related to lifestyle, social networks and health care use. Policies aimed at reducing mortality inequalities between older migrants and non-migrants should address the specific health needs of the various migrant groups, as well as socio-economic disparities.