Cranium bifidum is a congenital anomaly caused by abnormal development of the cephalic neural tube. We report two cases of cranium bifidum occultum with defects of both the frontal bone and anterior cranial base accompanied by infection and enlargement of frontonasal dermoid cysts. Surgery successfully interrupted the communication between the intracranial space and nasal cavity by inserting a pericranial flap after removal of the dermoid cysts. (C) 2011 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved.