4-fluoroamphetamine (4-FA) is a new stimulant psychoactive substance identified for the first time in Europe in 2008. Recently, 4-FA has been identified in driving under the influence of drugs population in Belgium [1] . However, postmortem data about 4-FA are sparse. The aim is to present the results of post-mortem toxicological investigations of a fatal road crash and discuss the 4-FA and cannabis influence. A 17 years-old male driver of a scooter died in a road crash, alone against a pole on the public road. The local prosecutor ordered an autopsy which allowed collecting hemothorax blood, cardiac blood, peripheral blood, bile, urine and gastric contents. He had no medical history. Biological specimens were submitted to standard toxicological analyses including screenings with UHPLC-MS/MS, UHPLC-DAD and GC-MS. GC-MS method was used to confirm fluoroamphetamine isomer. 4-FA was quantified with a specific and validated HPLC-MS/MS method on a 3200 QTRAP mass spectrometer. Sample preparation included a glacial acetonitrile/formic acid defecation. MRM transitions used were 154.1 > 109.3 and 83.1 for 4-FA and 199.2 > 165.2 for MDMA-D5 (internal standard). At autopsy, death was due to a high kinetic thoracic trauma, resulting in a major and rapid blood spoliation (rupture of the aortic isthmus and mediastinal rupture). Toxicological investigation only identified THC, THC-OH and THC-COOH (3.4, 0.9 and 10.6 ng/mL, respectively) and 4-FA (20.5 ng/mL) in peripheral blood. 4-FA was as well quantified in hemothorax blood (12 ng/mL), cardiac blood (28.5 ng/mL), bile (139 ng/mL), urine (1435 ng/mL) and gastric contents (100 ng/mL). 4-FA was responsible for a false-positive amphetamine EMIT urine testing (Atellica®, Siemens). While the cannabis influence was established, the influence of 4-FA was questionable at time of death. The high urine concentration associated to a low blood concentration of 4-FA was in favor of an old intake, more than 12 hours before death [2] . 4-FA pharmacokinetic/pharmacodynamics relationship is still not elucidated. Then, a review of drug users’ public internet forums revealed that 4-FA effects last about six hours, up to 12 hours. In conclusion, the influence of 4-FA was unlikely at the time of the accident. This case report provides analytical data that could support subsequent toxicological result interpretation in forensic cases involving 4-FA.