Are recessions good for health? A large existing literature using aggregate panel data suggests that the answer to this question is yes. However, this approach may be biased if people move in response to recessions. We offer direct evidence of this “migration bias” using a historical setting that provides both large-scale longitudinal microdata and an exogenous shock to local economic conditions. Using microdata to overcome migration bias, we find that the recession increased overall mortality. However, our estimates from aggregate data fail to recover this effect. Thus, in at least some settings, migration bias substantially affects results obtained from standard methodologies.