To ascertain the incidence of aortic dissection, we retrospectively studied the data base of our hospital (Ospedale di Treviso-ULSS n 10). The population in the Treviso area is well defined as a geographic settlement and was sufficiently stable from a demographic point of view in the period examined (1976-1988). Patients were selected on the basis of established aortic dissection diagnosed by angiography, surgical inspection or autopsy. One hundred eighty-seven patients were included: 126 of them lived in the hospital-referring area (mean annual population of 239824 people in the study period). The calculated incidence of aortic dissection was 40.4 new cases/million inhabitants/year. This figure is consistently higher than that reported in the literature. The outcome of the study is discussed and data are compared with those of previously published papers.