This article examines the impact of the introduction of ICD-10 on respiratory disease mortality statistics in England and Wales, specifically focussing on pneumonia, chronic lower respiratory diseases, and influenza. The main changes are highlighted and the article explains how figures can be adjusted to take account of these changes so that trends over time can be analysed. The number of deaths assigned to the respiratory disease chapter of the ICD as a whole decreased by 22 per cent as a result of the introduction of ICD-10. Although it is not usually recommended that comparability ratios from the CD-10 bridge-coding study are used to adjust rates prior to 1993, our analysis shows that unadjusted data for 1984 to 1992 can be used to examine longer time trends for respiratory diseases as a whole.