Although the number of elective operations for abdominal aortic aneurysms (AAA) is increasing, the sex- and age-standardised mortality rate of AAAs continues to rise, especially among men aged 65 years or more. The lethality of ruptured AAA continues to be 80-95%, compared with 5-7% by elective surgery of symptomfree AAA. In order to fulfil all WHO, European, and Danish criteria for screening, a randomised hospitalbased screening trial of 12,639 65-73 year old men in Viborg County (Denmark) was initiated in 1994. It seemed that US screening is a valid, suitable and acceptable method of screening. The acceptance rate was 77%, and 95% accept control scans. Furthermore, persons at the highest risk of having an AAA attend screening more frequently. We found that 97% of the interval cases developed from aortas that initially measured 2.5-2.9 cm - i.e. approx. only 5% attenders need re-screening at 5-year intervals. Two large RCTs have given clear indications of operation. Survivors of surgery enjoy the same quality of life as the background population, and only 2-5% of patients refuse an offer of surgery. Early detection seems relevant since the cardiovascular mortality is more than 4 times higher in AAA patients without previous hospital discharge diagnoses due to cardiovascular disease than among similar men without AAA. The absolute risk difference after 5 years was 16%. So, they will benefit from general cardiovascular preventive action as smoking cessation, statins and low-dose aspirin, which could inhibit further AAA progression. All 4 existing RCTs point in the same direction, viz. in favour of screening of men aged 65 and above. We found that screening significantly reduced AAA-related mortality by 67% within the first five years (NNT = 352). Restriction of screening to men with previous cardiovascular or pulmonary hospital discharge diagnoses would request only 27% of the relevant male population study to be invited, but would only have prevented 46.7% of the AAA-related deaths. However, the benefit was similar, and low risk screening reduced AAA specific mortality by 78% compared to 52% in the high risk group after 14 years. Despite attractive sustained benefit and improved cost effectiveness was reported by MASS trial after 10 years, cost effectiveness continues to be discussed. We found after 14 years that screening had reduced AAA-specific mortality by 66% (NNT = 135). The cost per life year gained was 157 euro [1,170 DKK] and the cost per QALY at 178 euro [1,326 DKK]. In all, the ethical dilemma of the prophylactic operation, and the limited psychological side effects seem not to outweigh the benefits of screening. Conclusively, we found that offering men aged 65-73 years screening for AAA seems acceptable according to criteria from WHO, Council of Europe, and the Danish National Board of Health. In US, UK, and Sweden national programmes are implemented. In Denmark, a flawed HTA from the region of Mid Denmark based upon an economic model, which excluded large AAAs, emergency operations of unruptured cases, and costs for intensive care beyond 48 hours are blocking a qualified decision. Future topics for will be creation and validation of multivariate models predicting need for later repair. We found AAA-size, wall calcification, smoking, tPA and antibodies against C. pneumoniae to be such candidates. Antibiotic treatment for chlamydial infection are disappointing, and we found no sign of C. pneumoniae in AAA walls but rather signs of proteins cross-reacting with chlamydial antibodies indicating "molecular mimicry" as an autoimmune reaction, which calls for further attention. More precise methods for measuring the degree of wall calcification must be developed and validated.