International trafficking in humans for sexual exploitation is an economic activity driven by profit motives. Laws regarding commercial sex influence the profitability of trafficking and may thus affect the inflow of trafficking to a country. Using two recent sources of European cross country data we show that trafficking of persons for commercial sexual exploitation (as proxied by the data sets we are using) is least prevalent in countries where prostitution is illegal, most prevalent in countries where prostitution is legalized, and in between in those countries where prostitution is legal but procuring illegal. Case studies of two countries (Norway and Sweden) that have criminalized buying sex support the possibility of a causal link from harsher prostitution laws to reduced trafficking. Although the data do not allow us to infer robust causal inference, the results suggest that criminalizing procuring, or going further and criminalizing buying and/or selling sex, may reduce the amount of trafficking to a country.