Recent international trends in asthma mortality among people aged five to 34 years were examined as a follow-up to an epidemic of asthma deaths in the late 1970s which appeared to be confined to New Zealand. Mortality rates were compared in 14 countries with suitable statistics; Australia, Canada, England and Wales, Finland, France, Japan, Israel, the Netherlands, New Zealand, Singapore, Sweden, Switzerland, the United States, and West Germany, for the period 1970 to 1984/5. In New Zealand, asthma mortality in this age group more than trebled from 1.3 per 100,000 in 1974 to 4.2 per 100,000 in 1979 and since then has declined substantially to 1.85 per 100,000 in 1985. Asthma death rates vary more than six-fold among the other countries examined, and although the New Zealand experience has not been seen to the same degree elsewhere, a gradual increase in reported asthma mortality has occurred since the mid to late 1970s in the majority of countries studied. The increase and subsequent decline in asthma mortality in New Zealand could not be explained by changes in diagnostic fashions or in the International Classification of Disease coding rules. Similarly, the US data do not suggest there is diagnostic transfer among diseases of airway obstruction. However, part of the differences in asthma mortality among the countries examined and the recent increases in asthma death rates, could be due to changing diagnostic fashions rather than true differences in mortality. International studies on the validity of asthma death statistics and on asthma prevalence are required to clarify these issues.