Differences between the number of AIDS death reported to the mortality register and to the AIDS register in Catalonia, Spain are relatively small, due to bot registers cooperation. Official mortality statistics are able to identify 78% of AIDS deaths. This proportion can be increased if the deaths caused by AIDS indicative diseases are included. The overall proportion of false positives when comparing both registers is 8.2%. Analysis of the available information from death certificates is useful to suggest simple recommendation to improve the quality of AIDS mortality data.