Background: A zero-tolerance law for driving under the influence of drugs (DUID) in Sweden led to a 10-fold increase in the number of cases submitted by the police for toxicological analysis. The statutory blood-alcohol concentration (BAC) limit for driving is 0.2 mg/g (∼0.02 g%). Methods: An in-house database (TOXBASE) was used to investigate re-arrests for impaired driving over 4 years (2001-2004), which comprised 36,799 cases. The age, gender, re-arrest rate of the offenders and the concentrations of ethanol and amphetamine in blood samples were evaluated. Results: We found that 44% of individuals (N = 16,277) re-offended 3.2 times on average (range 1-23 arrests). Between 85 and 89% of first-time offenders were men and there was also a male dominance among the recidivists (88-93%). The mean age of drunken drivers was ∼40 years compared with ∼35 years for driving under the influence of amphetamine, which was the drug identified in 50-60% of DUID cases, either alone or together with other licit or illicit drugs. The median BAC was 1.5 mg/g (∼0.15 g%), which suggests a dominance of heavy drinkers. The median BAC was even higher in recidivists (1.6-1.7 mg/g). The median concentration of amphetamine in blood was 1.0 mg/L in recidivists compared with 0.5 mg/L in the first-time offenders. About 14% of drunken drivers re-offended 1-10 times compared with 68% of DUID suspects, who were re-arrested 1-23 times. People with only a scheduled prescription drug in blood were re-arrested much less frequently (∼17%) compared with those taking illicit drugs (68%). Conclusions: The appreciable increase in number of arrests for DUID after a zero-tolerance law might reflect a heightened enthusiasm by the police authorities armed with knowledge that a prosecution is easier to obtain. Zero-tolerance laws do not deter people from impaired driving judging by the high re-arrest rates. During the sentencing of hardcore offenders, the courts should give more consideration to the underlying substance abuse problem. © 2007 Elsevier Ltd. All rights reserved.