The use of amphetamines in Brazil is common among truck drivers, which may be an important factor in the occurrence of traffic accidents. This article seeks to estimate the prevalence of amphetamine use among truck drivers. Drivers (N = 134) were stopped on two different highways in Sao Paulo state and they were asked to answer a questionnaire and provide a urine sample for toxicological analysis. All data were analyzed on Stata 8.0. All participants were males with low levels of schooling, whose mean age was 40.8 years. The presence of amphetamines was detected in 10.8% of all urine samples collected, being commonly justified in order to make truck drivers able to maintain their state of awareness. Amphetamine use was detected among truck drivers on Sao Paulo highways. The problem is that when the stimulant effects wear off, sleepiness due to sleep deprivation reduces concentration and good driver performance, making drivers vulnerable to traffic accidents and the related effects.