The rate of drug-facilitated sexual assault (DFSA; when an incapacitating drug is administered surreptitiously to facilitate sexual assault) is perceived to be increasing in the United Kingdom and elsewhere, causing international concern. This article examines evidence that quantifies the contribution of drugs in instances of alleged DFSA, identifies the substances involved, and discusses the implications of these findings. Of 389 studies examined, 11 were included in this review. The only study to consider covert drugging reported that 2% of alleged DFSA cases were attributable to surreptitious drug administration. Other studies failed to remove voluntary drug consumption from their cohort, biasing results. A study by the United Kingdom's National Forensic Services found no evidence to suggest that flunitrazepam (Rohypnol) had been used for DFSA during its 3-year investigation. In the United States, flunitrazepam is used recreationally, providing a likely explanation for its presence in samples of some alleged DFSA victims.