This study investigated patterns of illegal drug taking among Spanish drivers. The study was conducted in the fall of 1993 on 1500 drivers aged over 16, who properly completed and returned the questionnaires. The statistical SAS package was used. Among those surveyed, 23.5% had taken illegal drugs within their lifetime, 6.1% in the past year, 4.2% in the past month and 3.1% in the past week. Cannabis was the drug most frequently taking drug within lifetime (17.3%), the past year (3.4%), the past month (2.7%) or the past week (2.1%). Of those surveyed, 3% had driven after taking illegal drugs in the last year before the survey, and had been stopped during road checks (P < 0.001) and involved in road accidents (P < 0.0001) more often than those who had not driven under the influence of drugs. The study shows that driving under the influence of illegal drugs is somewhat frequent in Spain.