Most countries in the world impose some form of criminal sanctions on in-person sex work. Managers, clients, the sex workers themselves; the full or partial criminalisation of the in-person commercial sex market; the imposition of related sanctions such as upon loitering, management conceived as pimping, and collective work conceived as brothel keeping, the degree, capacity, and manner of criminalisation is varied. However, what remains consistent is the application of the criminal law itself. This is despite the uneven theoretical ground on which the application of such law rests. One of the most fundamental principles of the criminal law, ultima ratio, states that the law should only be applied as a last resort; the criminalisation of in-person sex work must be legally necessary to be justified. This essay examines the principle of ultima ratio with regards to in-person sex work through the application of two key concepts: subsidiarity and proportionality. On this basis, the argument that the criminal law is not an appropriate instrument for addressing the issue of in-person sex work is presented. Concluding remarks include recommendations for the application of a higher standard in our instrumentalization of the criminal law.