Aims: To compare the costs of hospital care and sick leave/disability pensions between two groups of driving while impaired (DWI) offenders: participants in an alcohol ignition interlock programme (AIIP) and controls with revoked licences, but with no comparable opportunity to participate in an AIIP. Setting: As an alternative to licence revocation DWI offenders can participate in a voluntary 2-year AIIP permitting the offender to drive under strict regulations entailing regular medical check-ups. The participants are forced to alter their alcohol habits and those who cannot demonstrate sobriety are dismissed from the programme. Participants: are liable for all costs themselves. Design: Quasi-experimental, with a non-equivalent control group used for comparison; intent-to-treat design. Based on the number of occasions/days in hospital and on sick leave/disability pension, the health-care costs for public insurance have been calculated. Finding: Average total health-care costs were 25% lower among AIIP participants (1156 individuals) than among controls (815 individuals) during the 2-year treatment period. This corresponds to over €1000 (SEK9610) less annual costs per average participant. For those who complete the 2-year programme the cost reduction was more pronounced; 37% during the treatment and 20% during the post-treatment period. Conclusions: The positive health-care effects were due apparently to reduced alcohol consumption. The social benefit of being allowed to drive while in the AIIP may also have contributed. The reduction in health-care costs was significant only during the 2-year treatment period, but among those who completed the entire AIIP sustained effects were also observed in the post-treatment period. The effects were comparable to those of regular alcoholism treatment programmes. (PsycINFO Database Record (c) 2012 APA, all rights reserved)(journal abstract)