Migration is a core component of population change and is both a symptom and a cause of major economic and social phenomena. However, data limitations mean that gaps remain in our understanding of the patterns and processes of mobility. This is particularly the case for internal migration, which remains under-researched, despite being quantitatively much more significant than international migration. Using the Scottish Longitudinal Study, this paper evaluates the potential value of General Practitioner administrative health data from the National Health Service that can be linked into census-based longitudinal studies for advancing migration research. Issues relating to data quality are considered and, using the illustrative example of internal migration by country of birth, an argument is developed contending that such approaches can offer novel ways of comprehending internal migration, by shedding additional light on the nature of both movers and the moves that they make.