This case describes a new feature of fetal brain death syndrome, abnormal movements mimicking fetal convulsions being subsequently found to be decerebrate hypertonicity in a brain-dead fetus. It also confirms the diagnostic criteria of fetal brain death, both clinical and ultrasonic. The development of polyhydramnios both prior to and after the presumed neurological event is suggested as an association with the diagnosis of fetal brain death. Increased awareness of this event and the heterogeneity of the presentation may prevent further unnecessary Caesarean sections, as to date only 4 of the 10 cases in the literature were diagnosed prenatally. Utilization of techniques such as fetal blood sampling should be considered to further delineate the diagnosis.