In Italy, the AIDS cases defined according to the CDC criteria are reported to the National AIDS Registry (RAIDS, compulsory surveillance system). The aim of the present study is to evaluate the completeness of AIDS cases reported and the quality of AIDS death certification in an Italian Region (Tuscany, about 3,500,000 inhabitants). The 737 AIDS cases reported to RAIDS as residents in Tuscany (1987-91) were cross-linked (key link: name and date of birth) with the data of the Mortality Registration system of the Region (RMR). For the residents in Tuscany decreased with a 279.1 death diagnosis (the code for AIDS deaths stated by the Italian Census Bureau) and not reported to RAIDS as AIDS cases, the clinical records were reviewed to check whether the diagnosis fitted the 1987-CDC diagnostic criteria. This study shows that there is a high completeness (97-98%) of the AIDS cases resident in Tuscany, reported to the RAIDS. The quality of RAIDS data is not as good with regard to life status assessment (23% of under-reporting of death). In Tuscany, the death certification for AIDS (code 279.1 of ICD IX) has a sensitivity of 88% and a specificity around 100% in comparison to RAIDS. About 50% of 'false negatives' in death certification are due to causes of death presumably unrelated to HIV infection. The evaluation of the quality of AIDS surveillance and mortality data is important in the assessment of the impact for AIDS epidemic in a target population.