This paper studies the effects of adding criminal offenders to a DNA database. Using a large expansion of Denmark's DNA database, we find that DNA registration reduces recidivism within the following year by up to 42 percent. It also increases the probability that offenders are identified if they recidivate, which we use to estimate the elasticity of crime with respect to the detection probability and find that a 1 percent higher detection probability reduces crime by more than 2 percent. We also find that DNA registration increases the likelihood that offenders find employment, enroll in education, and live in a more stable family environment.