Making the length of a prison sentence conditional upon an individual’s offence history is shown to be a powerful way of preventing crime. Under a law adopted in the Netherlands in 2001, prolific offenders could be sentenced to a prison term that was approximately 10 times longer than usual. We exploit quasi-experimental variation in application of the law across 31 cities to identify the effect on crime. We find the sentence enhancements to have reduced the rate of theft by 25%. The size of the crime-reducing effect is found to be subject to diminishing returns.