One hundred and forty-nine cases of hydramnios were detected among 13,750 parturients undergoing 25,000 routine ultrasonographic examinations. The prevalence of hydramnios was 1.08%. Ninety-seven patients (65.1%) had no apparent cause for the increased amount of fluid volume. Twenty-eight newborns (18.8%) were congenitally malformed, and 22 (14.8%) patients had diabetes mellitus. Rh incompatibility accounted for only 1.3% of the cases. It seems that with the improvement of modern obstetrics, mainly improving the antenatal management of diabetes and Rh incompatibility, there is a decrease in the relative incidence of these two conditions as etiological factors of hydramnios.