Several people have pointed out correctly that Preventing exacerbations in COPD (first published in DTB in July 2010 [DTB 2010; 48: 74–7] and reprinted in the BMJ in January 2011) included out-of-date definitions for the grades of severity of airflow obstruction. The definitions cited were those quoted in the 2004 National Institute for Health and Clinical Excellence (NICE) guideline on chronic obstructive pulmonary disease. The updated (2010) NICE guideline was published during the final stage of the production of the DTB article, and while the article text was amended accordingly to reflect the revised NICE recommendations on management of exacerbations, it failed to include NICE's revised definitions of severity of airflow obstruction. This error does not affect any of the DTB article's own recommendations.