Objectives Drug Facilitated Sexual Assault (DFSA) is defined by the covert administration of psychotropic substances to a victim in order to sexually abuse her or him. Most frequently used molecules are benzodiazepines, antihistamines, some neuroleptics and GHB. When delay between facts and sampling is too important for blood and urine analysis, hair can be an interesting alternative matrix to establish the involvement of drugs in the crime. However, the analysis and the interpretation may be tricky. The aim of this study is to present specific DFSA challenges through some case reports. Method In the pharmacology department of Garches Hospital, 3 locks of hair are used for a DFSA research. One strand is used to research 78 molecules in single LC-MS/MS technique (cocaine, amphetamines, designer drugs, opiates, benzodiazepines, some antihistamines and some neuroleptics). Another strand is used to search for cannabinoids by GC/MS. These two methods are fulfilled on 2 cm-length hair segments. The last strand is used to search for GHB by GC/MS on 5mm-length hair segments. Clinical case n° 1: A 15-year-old woman lodged a complaint against a friend of her and the boyfriend of the latter, for have been drugged and sexually abused 6 months before. 3 strands measuring approximately 32 cm each were collected from the victim. A significant increase of GHB was observed on three segments corresponding to the time of the facts. Clinical case n° 2 : A 10-year-old girl was admitted into intensive care unit for a moderate coma. The father admitted he drugged her daughter with GBL (GHB precursor). At her admission, GHB has been quantified in blood at 71 mg/L. The GBL bottle was also analyzed and was pure GBL. The father confessed that he tested the effects of the GBL to his wife a few days earlier. 4 weeks later, 4 strands were collected from the mother and her daughter. On the mother's hair, a significant increase of GHB was observed on the second segment, corresponding to the time of the facts. On the contrary, the undoubted take of GHB could not be highlighted in the daughter's hair. Clinical case n° 3: A 35-year-old woman who lived with a friend had a drink with him an evening. Afterward she felt dizzy, cold and lost consciousness. She lodged a complaint one month later. 4 strands of hair were collected. Several molecules were found on multiple segments of her hair : cocaine and metabolites, codeine, amphetamine, MDMA, MDA, pseudoephedrine, Hydroxyzine, cetirizine, doxylamine, diazepam, nordiazepam, temazepam, oxazepam, zolpidem, ketamine, cyamemazine, alimemazine, promethazine. Moreover, bromazepam was found only on the segment corresponding to the period of the facts at a concentration of 12 pg/mg, which could correspond to DFSA. But the question of the pharmacology effects of a single intake of benzodiazepine in a poly-addict person remains. Conclusion Hair is now an essential and unavoidable matrix in DFSA cases, but every analytical step can be delicate, especially the interpretation of findings. Though GHB research in hair has frequently been contested, these cases attest it can provide good results in such contexts. However, results may depend on the nature of the hair (hair color, age of the victim, texture,…) and negatives results must be interpreted very carefully, especially for children.