Abstract More knowledge about the impact of medication on driving are indicative of a lower likelihood of having a motor vehicle crash. The aim of this study was to investigate knowledge of professional drivers about the influence of driving impairing medicines in Serbia and Bosnia and Herzegovina. This multicenter cross-sectional study was conducted in 6 cities in Serbia and Bosnia and Herzegovina, during first trimester of 2017, with 221 professional drivers, using questionnaire with 35 statements, where participants expressed their agreement according to Likert scale, from completely disagree to completely agree. The average score related to the drivers’ knowledge was 131,58 (range from 49 to 175), 22,6% were unaware that some medicines may influence psychophysical abilities and ability to drive. A high percentage of participants in the study don’t know that a negative impact on the driving ability can be the result of the use of medicines from groups for which it is unexpected to have such effects, medicines that are dispensed without a medical prescription, herbal remedies, dietary supplements and medicines that affects eyesight or hearing. More than half didn’t know that medicines labeled with warning symbols Δ, ▲ and § are not allowed to be used immediately before or during driving. Professional drivers’ knowledge about driving impairing medicines is not satisfactory. Labeling system of these medicines is inadequate. These findings could help to identify drivers, who are at increased risk for using potentially impairing medicines, to inform and educate them, and to prevent driving under the influence of medicines.