Can incentives increase the use of HIV/AIDS testing in criminalized populations? Lawbreakers engaged in activities that place them at heightened risk of HIV/AIDS infection fear that engaging with the state to request an HIV test could increase their likelihood of incurring sanctions for violating the law. This article reports on a randomized field experiment that evaluates whether material incentives can spur lawbreakers to seek state assistance. Sex workers in Beijing, China, were randomly assigned to receive an in‐kind incentive equivalent to $1 (control group) or $15 (treatment group) for getting an HIV test. Fifteen dollars corresponds to the average amount a sex worker in the study might earn for one sexual transaction, and about 3 percent of her monthly earnings. The larger incentive increased HIV/AIDS testing rates by forty‐two percentage points, on average. Both low‐tier sex workers, who solicit on the streets and in brothels, and those in the middle tier, who work in karaoke bars and clubs, responded strongly to the large incentive. In addition, the large incentive was effective regardless of whether or not respondents were aware that prostitution is against the law. These findings suggest that modest incentives can have important effects among criminalized populations in authoritarian settings.