Little has been written regarding the ultrasonographic quantification of polyhydramnios or its subsequent management. Therefore, we designed this study to define polyhydramnios using the amniotic fluid index of greater than 2 SDs above the mean for late second- to third-trimester pregnancies, or 24 cm or greater. One hundred twelve nondiabetic women referred to Women's Hospital, Los Angeles County/University of Southern California Medical Center with the descriptive diagnosis of polyhydramnios made by experienced ultrasonographers were included in the study. There was poor correlation between these descriptions and fetal outcome. Twenty-six were qualitatively described as having severe, 29 as moderate, and 57 as mild polyhydramnios. Forty-nine of the 112 patients met our definition of significant polyhydramnios by having an amniotic fluid index of 24 cm or more. This particular definition allowed the inclusion of all fetuses with serious structural defects and/or death. Seven patients had an amniotic fluid index less than 24 cm, but with the traditional quantitative definition of one pocket of 8 cm or more; none of these patients had poor fetal outcome. These data appear to suggest that the use of descriptive definitions of polyhydramnios or a single fluid pocket of 8 cm or greater should be discarded in favor of using an amniotic fluid index of 24 cm or more. Once the diagnosis of polyhydramnios is made, the patient should have a detailed sonographic evaluation, be offered cytogenetic studies, and have antepartum surveillance.