A study of 1932 accidents that occurred during the transport of hazardous substances by road and rail from the beginning of the 20th century to July 2004 was carried out. The results obtained show an increase in the frequency of accidents over time. More than half of the accidents happened on roads (63%). The most frequent accidents were releases (78%), followed by fires (28%), explosions (14%) and gas clouds (6%). The various causes of the accidents, the type of substance involved and the consequences for the population (number of people killed, injured or evacuated) were also analysed. Among the diverse measures taken to improve this situation, the training of professional people involved in transportation seems to be of major importance.