Two cases of monochorionic diamniotic twin gestation with severe oligohydramnios-polyhydramnios sequence ('stuck' twin) are described. In each of these cases there was a marked fluctuation in amniotic fluid volume and reversal of which twin was 'stuck'. The definitive identification of the twins was evident due to a discordant fetal malformations in each twin pair. Copyright (C) 1996 International Federation of Gynecology and Obstetrics.