OBJECTIVES: We estimated the collective burden of mortality from autoimmune diseases among females in the United Kingdom and the effects of death certificate coding changes on this estimate. METHODS: We analyzed 1993-2003 England and Wales death certificate data for 3,150,267 females aged 1 year or older. We identified death certificates that listed autoimmune conditions as underlying or contributory causes of death. The percentages of all female deaths attributed to autoimmune disorders and to UK official mortality categories were ranked to determine the leading causes of death. RESULTS: In 2003, autoimmune diseases were the sixth or seventh most frequent underlying cause of death among females in all age groups below 75 years. Results were similar when both underlying and contributory causes of death were considered. The proportion of females dying with an autoimmune disorder remained relatively constant from 1993 to 2003. Analyses indicated that death counts for specific autoimmune diseases had been underestimated. CONCLUSIONS: Autoimmune diseases are a leading cause of death among females in England and Wales, but their collective impact remains hidden in current disease classification systems. Grouping these disorders together may help promote research needed to identify common determinants and future prevention strategies.