Although the Centers for Disease Control and Prevention currently only recommend daily dosing of HIV preexposure prophylaxis (PrEP), an on-demand PrEP dosing strategy that includes doses before and after sexual activity has been shown to reduce risk for HIV acquisition in men who have sex with men. In this letter, we report a case of HIV infection and drug resistance in a patient using PrEP outside of regular clinical care, adopting a sporadic, suboptimal dosing strategy with pills he obtained from his sexual partners. This case illustrates the potential risks of PrEP use without provider monitoring to ensure safe and effective dosing and laboratory follow-up, as well as key challenges that must be addressed as non-daily PrEP use becomes more common outside of controlled research settings.