Two cases of blindness following paranasal sinus surgery are presented. The first patient, a 38-year old man, developed a delayed massive haemorrhage, after bilateral sphenoethmoidectomy. This hemorrhage could be stopped by electric cauterisation under endoscopical control. During this reintervention the patient developed total blindness of his right eye, and a restriction of the inferotemporal left visual field. The second patient, a 10-year old girl, developed, after bilateral spheno-ethmoidectomy for isolated sphenoiditis, total blindness of the left eye and paralysis of the ipsilateral extraocular muscles. According to the literature, blindness secondary to paranasal surgery is mainly due to retrobulbar hemorrhage. In the first case blindness was due to a direct cauterisation of the optic nerve, after perforation of the lamina papyracea. In the second case, blindness was probably due to a hemorrhage in the orbital apex.