The records of all patients with abdominal aortic aneurysms (AAAs) in a Midwest city with a stable population over a 30-year period were reviewed. There were 296 patients (196 men and 100 women) for an incidence of 21.1 aneurysms/100,000 person-years. The median age at diagnosis was 69 years for men and 78 years for women. Seventy-eight percent of patients were asymptomatic at the time of diagnosis; their aneurysms were incidental findings. Rupture occurred in 60 patients (20.3%). Thirty-six patients (12.2%) had rupture of the aneurysm as the presenting complication. For previously diagnosed aneurysms that subsequently ruptured, the average period from diagnosis to rupture was 48.7 months. Rupture occurred in only two aneurysms smaller than 5 cm. The overall mortality rate from rupture was 15.5%. Evaluation of data (including autopsy reports) by decade revealed an absolute increase in the incidence of AAAs in the population under study. More aneurysms of all sizes occurred from 1971 to 1980 than in the previous two decades combined. Although ultrasound examination has increased the detection of small aneurysms, the incidence of aneurysms 7 cm or larger at the time of diagnosis has also increased; the frequency of rupture was greatest in the last decade. To compare the data of the population-based study with the statistics for patients seen in a referral practice, the records of 616 patients from a referral population were also reviewed. In the referral population the ratio of men to women was 5:1, and the age at diagnosis was lower for both groups.(ABSTRACT TRUNCATED AT 250 WORDS)