How can districts become totally embedded in informal economy despite harsh state regulation? In this paper, we use qualitative and quantitative data to explain the increasing number of "clandestine" street prostitutes in Paris during The Belle Epoque. We first describe the economics of street prostitution at the time: street prostitutes were young, unskilled and well-paid; they tended to work with pimps that were from the same area and clustered in neighborhoods where they could compete with regulated brothels. Street prostitutes not only generated profits for themselves but also for a whole bunch of actors, thereby switching the whole local economy to this industry, at the expense of the formal economy.