In this study, we examine the impact of ethnic diversity in Danish municipalities on citizens’ social trust over the last three decades. During this period, Danish society has grown increasingly ethnically diverse, and this begs the question whether this has influenced trust in others negatively. Existing evidence from the Anglo-Saxon countries would suggest that this is the case, whereas evidence from the European continent mainly suggests that no link exists between ethnic diversity and social trust. The empirical analysis uses individual-level data on social trust from several surveys in Denmark in the period from 1979 to 2009 coupled with diversity at the municipality level. Individual-level measures of trust over time enable us to estimate the impact on social trust of changes in ethnic diversity within municipalities and, we argue, thereby obtain a more precise estimate of the effect of ethnic diversity on trust. The results suggest that social trust is negatively affected by ethnic diversity. We conclude by discussing this result and suggest avenues for further research.