This paper discusses the limitations of harmonised sampling designs for survey research on immigrants in Germany and the Netherlands. Although the concepts for immigrants are largely similar in both countries, there are severe constraints when it comes to comparable sampling designs. While in the Netherlands a sample can be drawn from a national population register by Statistics Netherlands, this is impossible in Germany due to the decentralised setup of the population register and legal restrictions on merging existing databases. Harmonisation of immigrant statistics is thus less a problem at the concept level than in the implementation. Achieving a harmonised data collection on immigrants for Germany and the Netherlands will be a major challenge.