Evidence-based risk-prevention policies for people involved in prostitution require that reliable population estimates are built. This study proposes a methodological framework and novel data source for measuring their population in regions where the internet plays a predominant role in the industry. We derive single registration capture-recapture population estimates using the Zelterman approach. The resulting estimates for the Netherlands and Belgium are lower than previous rough estimates. We find that relative to the overall population of the two countries, the proportion of sex workers are roughly identical despite differing legal environments
