During the years 1964-1985, a total of 89 patients were operated on for aortic dissection: 55 were treated for proximal dissection and 34 for distal dissection of the aorta. In the former group a diagnostic delay more than 24 hours after hospitalization occurred in 17 instances (31%), and in the latter group in 18 instances (53%). The most common incorrect diagnosis in both groups was myocardial infarction. In the proximal group of aortic dissection, other cardiac diseases suspected were pericarditis, endocarditis and congestive heart failure. In the distal group of aortic dissection, acute surgical abdomen was the most common cause of incorrect diagnosis after ischaemic heart disease. Four case reports with diagnostic delay are presented.