The study of multiple causes of death helps reveal the true extent of mortality statistics. The aim of this study was to assess trends in asthma mortality rates in the city of Rio de Janeiro, Brazil, from 2000 to 2009, based on data from the Mortality Information System among individuals one year or older, in which asthma was mentioned on any line or in any part of the death certificate. Linear regression was used for data analysis. The historical series showed a downward trend in the standardized mortality rate related to asthma as the underlying or associated cause of death, with a reduction in males and stability in females. When asthma was the underlying cause, the most common associated causes were diseases of the respiratory system. Asthma-related mortality was underestimated when considered only as the underlying cause, which could be avoided by the use of a multicausal methodology in asthma mortality statistics.