This paper derives a gravity equation for commuter flows from a simple spatial labor market model, and uses it to identify the effect of regional borders on commuting. This structural approach allows us to identify the relevant control variables and sources of potential omitted variable bias. The model is estimated by means of a negative binomial regression using Belgian data on intermunicipality commuting. We find that regional borders exert a sizable residual deterrent effect on commuting. This border-effect differs significantly between regions and depends on the direction in which the border is crossed.