Osteomata of the paranasal frontal and ethmoidal sinuses are benign, slow growing tumors generally asymptomatic. Complications due to orbital or intracranial development of the osteoma are rare and demand neurosurgical treatment. The authors report two cases. In the first a fronto-ethmoidal osteoma first caused exophtalmos and later ophtalmoplegia due to compression of the superior ophtalmic vein. In the second case the posterior development of an osteoma of the frontal sinus resulted in pneumocephalus with epileptic fits and headache and initially homolateral hemiparesis. In both cases CT Scan showed the extent of the osteoma and in the second case the gap in the wall of the sinus. Both osteomata were radically removed through frontal craniectomy. The literature is reviewed, 12 other cases of pneumocephalus due to posterior development of paranasal osteomata have been published during the last 50 years.