Traffic accidents are responsible for 1.25 million deaths worldwide and are the most common cause of death among those aged 15-29 years. In Brazil, traffic accidents caused more than 44,000 deaths in 2014. The use of psychoactive drugs is an important risk factor for being involved in traffic accidents. Previous studies have found that psychoactive substances are commonly used by truck drivers in Brazil to maintain their extensive work schedule and stay awake while driving during nighttime hours. The state of Sao Paulo is one of the most important states regarding goods transportation. Important highways cross through Sao Paulo to other regions from Brazil and to other countries in Latin America. This study aims to determine the prevalence of illicit drug use by truck drivers in the state of Sao Paulo through toxicological analyses of oral fluid. Truck drivers were randomly stopped by police officers on federal roads during morning hours. Oral fluid samples were collected using the Quantisal™ device. In addition, a questionnaire concerning sociodemographic characteristics and health information was administered. Oral fluid samples were screened for amphetamine, cocaine, and tetrahydrocannabinol (Δ9-THC) by ELISA and the confirmation was performed using ultra performance liquid chromatography with tandem mass spectrometry detection (UPLC-MS/MS). Of the 764 drivers stopped, 762 agreed to participate. The participants were driving an average of 614km and 9.4h a day. Of the total samples, 5.2% (n=40) tested positive for drugs. Cocaine was the most frequently found drug (n=21), followed by amphetamine (n=16) and Δ9-THC (n=8). All drivers were men with an average age of 42.5 years. With these results we were able to verify that many truck drivers were still consuming psychoactive drugs while driving, and cocaine was the most prevalent one. This reinforces the need for preventive measures aimed at controlling the use of illicit drugs by truck drivers in Brazil., (Copyright © 2017 Elsevier B.V. All rights reserved.)