Although federal legislation for the implementation of sex offender registration and notification systems is now a decade old, empirical studies on the efficacy of this policy are relatively nonextant. This article explores the impact of registration legislation on the incidence of forcible rapes. Using monthly count data of rapes aggregated at the state level, this analysis uses Box-Jenkins autoregressive integrated moving average (ARIMA) models to conduct 10 intervention analyses on the enforcement of Megan's Law. The results of the analyses are mixed on whether the enforcement of sex offender registration had a statistically significant effect on the number of rapes reported at the state level. Although several states showed a nonsignificant increase in the number of rapes, only three states had a significant reduction in rapes. Policy implications are discussed in terms of the efficacy of sex offender registration and whether changes in these laws should be considered. © 2008 Sage Publications.