Creutzfeldt-Jakob Disease (CJD) is a rare pathology (about 1 case per million) but it has a great importance for Public Health; the Italian National CJD register has been established in the Istituto Superiore di Sanita (ISS) since 1993, and epidemiological studies on CJD have been carried out as well. This paper reports a mortality study carried out comparing and integrating data from the two available sources: the National CJD Register and the Italian Data Base on Mortality, processed by the ISS Statistics Unit, on the data collected by the Italian Census Bureau (ISTAT). The study allowed to estimate: the underreporting of CJD mortality to both sources, the misclassification of ISTAT data and the integrated mortality rates from CJD in Italy: 1.58 per million persons aged 25 or more, average rate during the period 1993-1999.