Using publicly available UK police data and census areal level data on ethnicity, we explore the connection between frontiers separating neighbouring areas identified as having significantly different ethnic distributions and overall crime levels. We develop a new approach using Bayesian spatial statistical methods that permit asymmetries in spatial effects and allow for spatial autocorrelation in the data. We illustrate our method using data on Sheffield and find clear evidence of ‘open’ frontiers. Permutations tests and Poisson regressions with fixed effects reveal compelling evidence that social frontiers are associated with higher rates of crime.