Lysergic acid diethylamide (LSD) is a potent hallucinogen, active at very low dosage and its determination in body fluids in a forensic context may present some difficulties, even more so in hair. A dedicated liquid chromatography–electrospray-tandem mass spectrometry (LC–ES-MS/MS) assay in hair was used to document the case of a 24-year-old man found dead after a party. Briefly, after a decontamination step, a 50 mg sample of the victim's pubic hair was cut into small pieces (<1 mm length), and incubated overnight in 3 mL of phosphate buffer pH 5 at room temperature. After a liquid–liquid extraction (dichloromethane/ether), the extract was analyzed using a LC–ES-MS/MS method exhibiting a limit of quantification of 0.5 pg/mg for LSD. A LSD concentration of 0.66 pg/mg of pubic hair was observed. However, this result remains difficult to interpret owing to the concomitant LSD presence in the victim's post mortem blood and urine, the lack of previously reported LSD concentrations in hair, and the absence of data about LSD incorporation and stability in pubic hair.