The use of a drug to modify a person’s behavior for criminal gain is not a recent phenomenon. However, the recent increase in reports of drug-facilitated crimes (sexual assault, robbery) has caused alarm in the general public. Drugs involved can be pharmaceuticals such as benzodiazepines (flunitrazepam, lorazepam, etc), hypnotics (zopiclone, zolpidem), sedatives (neuroleptics, some histamine H1 antagonists), or anesthetics (γ-hydroxybutyrate, ketamine), drugs of abuse such as cannabis, ecstasy, or lysergide, or more often ethanol. Drugs used to facilitate sexual assaults can be difficult to detect (active products at low dosages, chemical instability), possess amnesic properties, and can be rapidly cleared from the body (short half-life). In these situations, blood or even urine can be of little interest. This is the reason why this laboratory developed an original approach based on hair testing. Hair was suggested as a valuable specimen in situations where, as a result of a delay in reporting the crime, natural processes have eliminated the drug from typical biologic specimens. Although there are many papers focused on the identification of drugs in hair following chronic drug use, those dealing with a single dose are very scarce. The experience of the authors is documented in cases involving zolpidem, GHB, lorazepam, methylenedioxymethamphetamine, and flunitrazepam. The expected concentrations in hair are in the low picogram per milligram range for the hypnotics. Drug exposure is demonstrated by hair segmentation. Hair analysis may be a useful adjunct to conventional drug testing in sexual assault. It should not be considered as an alternative to blood and urine analyses but as a complement. MS/MS technologies appear to be a prerequisite.