Amniotic fluid is the product of complex and dynamic fetal and placental physiologic processes. Disruption of the fine balance may result in overproduction or underproduction of fluid. Therefore, alterations in amniotic fluid volume serve as important markers of both in utero developmental defects as well as physiological responses to fetal hypoxemia and other metabolic disturbances such as maternal/fetal hvperglycemia. Both polyhydramnios and oligohydramnios may be associated with either major congenital anomalies or adverse perinatal outcomes. Although the ultrasonographic diagnostic criteria have yet to be firmly established, it is apparent that both subjective and objective criteria have been used successfully to identify these conditions. Polyhydramnios, particularly when severe and detected early in gestation, can be treated antenatally with serial amniocenteses. Oligohydramnios with intact membranes, especially when severe and in the absence of anomalies, is usually managed by delivery; however, further research is indicated to delineate management guidelines.