In the late nineteenth century, the French colonial government legalized prostitution in French-controlled areas of Tonkin. Although the colonial state tolerated prostitution, state regulations forced sex workers to register with the state and limited sex workers’ profits, mobility, and freedom. Consequently, a black market for clandestine unregistered prostitution developed, enabling workers to evade state restrictions. This article asserts that during the inter-war years (1920–1945) unregistered sex workers used Ả Đào music houses as fronts for clandestine prostitution. The colonial state attempted to curb illegal activities in various ways, but clandestine prostitutes easily evaded the state. By the late colonial era, Ả Đào music’s association with prostitution had damaged its reputation.