A newborn infant who suffered intra-uterine anoxia is described, whose mother inhaled butane gas accidentally during the sixth month of pregnancy. The infant was born at 39 weeks. Ultrasonography and neuroradiological studies (CT scan and angiography) showed an almost complete absence of both cerebral hemispheres. The thalamus, brainstem and cerebellum were preserved. These findings were compatible with hydranencephaly. The authors believe that the malformation was due to intra-uterine anoxia occurring during fetal brain-development.