OBJECTIVE Population-based screening for abdominal aortic aneurysms (AAAs) in elderly men is organized in many regions and countries in the Western world, and the prevalence of disease is reported to decline. Whether the prevalence among those with a family history also is declining is unknown. The primary purpose of this study was to assess the prevalence of AAAs among siblings of persons with AAAs and to investigate the proportion of siblings already diagnosed by opportunistic screening. METHODS Patients treated for AAAs from January 2008 through December 2010 (n = 412) in Stockholm, Sweden, were screened for siblings. Seven hundred seventy-nine siblings were identified. All siblings <80 years residing in Stockholm County were considered eligible and were invited to participate in the study (n = 174). Deceased siblings were not included in the study, regardless of the cause of death. One hundred fifty siblings were enrolled in the study after informed consent was provided. One hundred thirty-four siblings were screened for AAAs with ultrasound scan and maximum aortic, infrarenal, anteroposterior, external (outer-to-outer) aortic diameter was measured. Characteristics of siblings with and without AAAs were compared. RESULTS The mean age of the screened siblings was 66.4 years (standard deviation, 7.1). Of the siblings, 11% were found to have an AAA, 17% (n = 11) of the brothers, and 6% (n = 5) of the sisters. Only 11% of the siblings were screened for AAAs before the study. One of 16 siblings with AAAs was <65 years. Ever smoking was evident in 81% of the AAA siblings compared to 59% in the non-AAA siblings. Factors associated with increased risk of AAAs in the multivariate regression analysis were: male sex (odds ratio, 3.4; 95% confidence interval, 1.1-10.8; P = .04) and age >65 (odds ratio, 10.8; 95% confidence interval, 1.3-86.4; P = .03). Ever smoking was not statistically significant as a risk. CONCLUSIONS A strikingly high prevalence of AAAs in siblings was found as compared to the reported declining aneurysm prevalence in elderly men in the Western world. Systematic improvements regarding screening of first-degree relatives is mandated and selective screening of siblings is an underused tool to prevent death from aneurysm disease, both among men and women.