The occurrence of clinically diagnosed and/or ruptured abdominal aortic aneurysms (AAAs) in the families of 220 patients with AAAs, treated at the Surgical Clinic, University Hospital of Umeå in the northern part of Sweden during the years 1965-82, was studied. A questionnaire concerning the blood relatives was answered by 87/89 patients. 16/87 patients (18%) had blood relatives with AAAs. In 14 families one blood relative was affected, and in 2 families two blood relatives were affected. First degree relatives were affected in 9/87 cases (10%), and second degree relatives in 7/87 cases (8%). 9/468 (1.9%) of the patients' brothers and sisters but only five of all their cousins had AAAs, and 7/204 (3.4%) of the dead brothers and sisters had died of ruptured AAAs. Concerning the patients who were not included in the letter survey at least 14/133had blood relatives with AAAs. However, the great majority of these patients were dead when the study was performed and could not be asked aboutthe occurrence of AAAs in their families. The patients with AAAs had significantly higher serum concentrations of triglyceride and (YLDL + LDL)-cholesterol and a significantly lower serum concentration of HDL-cholesterol than randomly selected healthy controls of the same sex and age as the patients. We also compared the distributions of genetic markers (HLA antigens, the blood group systems ABO, Rh, MNSs, P, Kell, Lewis and Duffy and the serum protein group systems haptoglobin, transferrin, group-specific component, complement C3, properdin factor and alpha-1-antitrypsin) in patients with AAAs with the distributions in controls and in some cases with the expected distributions according to the Hardy-Weinberg law. A significantly decreased frequency of Rh-negative individuals, and significantly increased frequencies of Kell-positi ve individuals, of MN heterozygotes and of heterozygotes concerning haptoglobin type was found. Furthermore, the aneurysm walls of patients with and without AAAs in the family were compared concerning the morphology, but no differences were found. We also studied the occurrence of collagen types I and III in the aneurysm walls, and the occurrence of vimentin and desmin in the smooth muscle cells of the aneurysm walls, but all these components were present in the aneurysm walls of both the patients with and those without AAAs in the family. To summarize the results, there seems to be an increased frequency of AAAs, and especially of ruptured AAAs, among the brothers and sisters of patients with AAAs. Elevated serum concentrations of triglyceride and (VLDL + LDL)- cholesterol and a lowered serum concentration of HDL-cholesterol seems to be common in patients with AAAs. There seems to be a hereditary predisposition to the development of AAAs, because we found associations with four different genetic markers (Rh, MN, Kell, haptoglobin group). However, there is probably no specific "familial" type of AAAs, because we found no differences between the patients with and those without AAAs in the family.Key words: / <p>S. 1-42: sammanfattning, s. 43-103: 5 uppsatser</p> / digitalisering@umu