Divorce rates are higher in cities. Based on Danish register data, this paper shows that of the marriages formed in the city, those couples who remain in the city have a 23% higher divorce rate than those who move out. In this paper, we test whether this observation is due to sorting of more stable marriages into rural areas or if there exists a causal effect of living in urban areas on marriage instability. Our identification strategy supplements the timing-of-events approach with an instrumental variable. Our findings suggest that the effect of living in an urban area on the divorce risks drops substantially and loses statistical significance once we address sorting. © 2009 the editors of the Scandinavian Journal of Economics.