The aim of this study was to determine the normal values for aortic diameters and the prevalence of aortic dilatation in a mixed Turkish population. Between March 1998 and May 2000, patients who were undergoing abdominal ultrasonography examination for pathologies not involving the aorta, in three different cities, were enrolled into the study prospectively. The anterior posterior aortic diameters were measured at the subdiaphrogmatic and aortic bifurcation levels using ultrasonography. A total of 596 patients were included (302 females, 294 males). The mean age was 48 +/- 16 years (range, 6 - 88 years). The mean aortic diameter in the whole group was 19.0 +/- 3.9 mm (10 - 45 mm) at the subdiaphragmatic level and 15.7 +/- 3.6 mm (9 +/- 65 mm) at the aortic bifurcation level. The mean subdiaphragmatic aortic diameter was 18 +/- 3 mm in females and 19 +/- 4 mm in males. The mean aortic diameters at the bifurcation level was 15 +/- 3 mm in females and 16 +/- 4 mm in males. An aortic bifurcation diameter > 30 mm was encountered in 0.67% of the population. This ratio increased to 1.8% in patients over 55 years of age, regardless of sex. A subdiaphragmatic aorta diameter above 30 mm was observed in 1.2% of the population. In patients over the age of 55 years, this ratio increased to 2.7% (3.6% in males and 1.9% in females). In this national study, the subdiaphragmatic aortic diameters were similar to mean values reported in the world literature. The mean aortic bifurcation diameters were generally lower when compared with the literature, which may be due to difficulties in standardization of the measurements. Aneurysmal dilatation rates in this study also conform to those reported in studies conducted in other countries. Considering the significant number of patients with aneurysmal dilatation of the aorta in the elderly population, we believe it would be prudent to evaluate the aorta in all patients undergoing abdominal ultrasonographic examination.