The aim of this study was to investigate the scale and network structure of prostitution in the northern provinces of the Netherlands. This study tries to answer three research questions – using a social network analysis – about (1) the size of the prostitution network, (2) the formation of subgroups, and (3) key positions within the networks. The findings show that approximately two thirds of the researched prostitution networks is still unregistered, while there are indications that the outcome of the estimate is in line with the actual situation. Furthermore, results show that prostitutes have a tendency to form subgroups on the basis of the same nationality, which indicates that homophily plays a role in the formation of subgroups. The identification of the actors who occupy key positions in the network were based on the key player problem (KPP). A striking finding was that organizers of prostitution (such as pimps) did not have a central position in the networks. These findings provide insight into the way in which prostitution is registered, and provide points of departure for interventions to disrupt the network or, on the contrary, to strengthen it.