Objective: To assess whether screening for abdominal aortic aneurysms in men r educes mortality. Design: Population based randomised controlled trial of ultras ound screening, with intention to treat analysis of age standardised mortality. Setting: Community based screening programme in Western Australia. Participants: 41 000 men aged 65-83 years randomised to intervention and control groups. Int ervention: Invitation to ultrasound screening. Main outcome measure: Deaths from abdominal aortic aneurysm in the five years after the start of screening. Resul ts: The corrected response to invitation to screening was 70%. The crude preval ence was 7.2%for aortic diameter ≥.30 mm and 0.5%for diameter ≥.55 mm. Twice as many men in the intervention group than in the control group underwent elect ive surgery for abdominal aortic aneurysm(107 v 54, P=0.002, χ2 test). Between scheduled screening and the end of follow up 18 men in the intervention group an d 25 in the control group died from abdominal aortic aneurysm, yielding a mortal ity ratio of 0.61(95%confidence interval 0.33 to 1.11). Any benefit was almost entirely in men aged between 65 and 75 years, where the ratio was reduced to 0.1 9(0.04 to 0.89). Conclusions: At a whole population level screening for abdomina l aortic aneurysms was not effective in men aged 65-83 years and did not reduce overall death rates. The success of screening depends on choice of target age g roup and the exclusion of ineligible men. It is also important to assess the cur rent rate of elective surgery for abdominal aortic aneurysm as in some communiti es this may already approach a level that reduces the potential benefit of popul ation based screening. Objective: To assess whether screening for abdominal aortic aneurysms in men r educes mortality. Design: Population based randomized controlled trial of ultrasound screening, with intention to treat analysis of age standardized mortality. Setting: Community based screening program in Western Australia. Participants: 41 000 men aged 65-83 years randomized to intervention and control groups. Int ervention: Invitation to ultrasound screening. Main outcome measure: Deaths from abdominal aortic aneurysm in the five years after the start of screening. Resul ts: The corrected response to invitation The crude preval ence was 7.2% for aortic diameter ≥.30 mm and 0.5% for diameter ≥ 0.55 mm. Twice as many men in the intervention group than in the control group underwent elect ive surgery for abdominal aortic aneurysm (107 v 54, P = 0.002, χ 2 test). Between scheduled screening and the end of follow up 18 men in the intervention group an d 25 in the control group died from a biliary aortic aneurysm, yielding a mortal ity ratio of 0.61 (95% confidence interval 0.33 to 1.11). Any benefit was almost entirely between men aged 65 and 75 years, where the ratio was reduced to 0.1 9 (0.04 to 0.89). Conclusions : At a whole population level screening for abdomina l aortic aneurysms was not effective in men aged 65-83 years and did not reduce overall death rates. The success of screening depends on choice of target age g roup and the exclusion of ineligible men. It is also important to assess the cur rent rate of elective surgery for abdominal aortic aneurysm as in some communiti es this may already approach a level that reduces the potential benefit of popultion based screening.