Background. Self-asphyxiation using car exhaust gas is a common method of suicide in England and Wales, particularly in young males. The introduction of catalytic converters has reduced the toxicity of car exhausts. The main aims of the study were: to seek evidence of a fall in car exhaust suicides in the general population and in age and gender groups; to relate any fall to changes in car exhaust systems, particularly since legislation on car exhaust emissions in 1993; and to examine rates of suicide by other methods for evidence of method substitution.

Methods. Population study in England and Wales using national suicide statistics for 1987 to 1998.

Results. There was a fall in suicide by car exhaust asphyxiation in all age and gender groups. This change was most marked after 1993. The overall population suicide rate (all methods) also fell but there was no overall change in suicides by young males or females. In these groups suicide by hanging increased.

Conclusions. Legislation on catalytic converters appears to have contributed to a fall in car exhaust suicides. However, the effect on overall suicide rates in young people has been reduced by method substitution.