Background. The legal definition of suicide in England and Wales (E & W) gives rise to a high proportion of open verdicts and an underestimated suicide rate. We examined whether the ratio between open and suicide verdicts in E & W has changed between 1974 and 1991 and whether it varies according to coroners' qualifications.

Methods. Temporal changes of the ratio of open and suicide verdicts were examined using logistic regression adjusting for confounders such as changing age and gender distributions of suicide victims and the methods they use.

Results. Adjusted for age at death and suicide method, the ratio between open and suicide verdicts had, over successive 3-year time periods, increased with a factor 1·21 (95% CI 1·20–1·23) for male and 1·15 (95% CI 1·14–1·17) for female deaths. Medical coroners were 1·25 (1·08–1·44) times more likely than non-medical coroners to return open rather than suicide verdicts.

Conclusions. As a likely result of factors in the death registration system, the ratio between open and suicide verdicts has increased substantially in E & W since the early 70s. In 1990 it was higher than in any other comparable country. This has important implications for comparisons of time trends in suicide between E & W and other countries.