In 2017, California officially became a sanctuary state following the passage of Senate Bill 54, which limits state and local police cooperation with federal immigration authorities. Following the passage of SB54, critics worried that crime rates would rise. What impact did this policy have on crime in California? The current study, the first of its kind, addresses this question. Using a state-level panel containing violent and property offenses from 1970 through 2018, we employ a synthetic control group design to approximate California’s crime rates had SB54 not been enacted. We interpret the gap between California’s 2018 crime rate and its synthetic counterfactual as SB54’s impact. Results show that SB54’s impact on violent and property crime is neither robust nor sufficiently large to rule out a null effect. Sensitivity analyses buttress this finding. We discuss the implications of the findings for crime policy in the U.S.