Criminals illegally obtaining firearms represent a great risk to many urban residents. This cross-sectional study of 54 US cities uses data on state laws governing gun sales, a survey of law enforcement agencies’ practices to promote compliance with gun sales laws, and crime gun trace data to examine associations between these policies and practices with gun trafficking indicators. Higher levels of local gun ownership were linked with greater intrastate gun trafficking. Regression models estimate that comprehensive regulation and oversight of gun dealers and state regulation of private sales of handguns were each associated with significantly lower levels of intrastate gun trafficking. Discretionary permit-to-purchase licensing laws’ negative association with intrastate trafficking disappeared when local gun ownership is controlled. The effects of these relatively restrictive gun purchase laws on trafficking may be mediated by the laws’ lowering of gun ownership. Relatively low prevalence of gun ownership may also be a prerequisite for passage of discretionary purchase. We observed no effect on intrastate trafficking of laws limiting handgun sales to a maximum of one per person per month.