Since abdominal ultrasonography has become a routine diagnostic procedure, increasing numbers of small asymptomatic abdominal aortic aneurysms are detected incidentally. Of 128 patients (108 male, 20 female) with abdominal aortic aneurysms, 96 patients were observed clinically and by repeated ultrasound studies for an average of 3.47 years, adding up to a total observation period of 333 patient-years. Among these 96 patients, 72 had small aneurysms (averaged diameters less than 5 cm). Three of them were lost to follow up. None of the remaining 69 patients died from rupture, 20 died from other causes and 8 patients were successfully operated. Of the patients with a large aneurysm one was lost to follow up. Five patients of the remaining 23 died as a result of rupture, 7 were successfully operated. The average growth rate of small aneurysms was 0.18 cm/year, whereas the larger aneurysms showed a growth rate of 0.28 cm/year (diameter). The survival rate of patients with small aneurysms was 94% after one year, 80% after 3 years, and 73% after 5 years, indicating that life expectancy is reduced in patients with an aneurysm of the abdominal aorta, but not because of complications of the aneurysm.