Using individual data on persons arrested in the Medellin Metropolitan Area, this paper assesses whether the change in punishment at age 18, mandated by law, has a deterrent effect on arrests. No deterrent effect was found on index, violent or property crimes, but a deterrence effect was found on non-index crimes, specifically those related to drug consumption and trafficking. The change in criminal penalties at 18 years of age does not explain future differences in human capital formation among the population that had been arrested immediately after versus immediately before reaching 18 years of age. There is no evidence that the longer length of time to recidivate on the part of individuals arrested for the first time immediately after reaching 18 implies future differences in human capital formation. These results suggest a specific deterrence effect resulting from the harsher experience while in prison of those arrested right after reaching 18.