&NA;Intracranial extradural pressure (ICP) was monitored by using a miniaturized transducer for an average period of 8 days after direct operation in 55 patients with ruptured cerebral aneurysms. Acute stage operation and drainage of cerebrospinal fluid were simultaneously performed in most of the patients. In many grade I patients with satisfactory cisternal drainage, ICP was monotonously stable, with faint pressure waves. When the drained fluid volume decreased or drainage was removed, however, ICP was elevated moderately, with associated pressure waves present. There were no A‐waves observed in any of the patients. Decreases of mean ICP and disappearance of pressure waves were found 2 to 3 hours after infusion of 200 or 300 ml of 10% glycerol or 20% mannitol in patients without drainage or with an inadequate drain, but were not found in patients with a good drain. In a patient showing diffuse severe vasospasm, a rapid elevation of ICP caused by marked brain edema was observed. In patients with residual aneurysms or incompletely clipped aneurysms, ICP increased immediately after rupture of these aneurysms. The daily mean ICP was higher in patients with a clinically poor condition and/or severe subarachnoid hemorrhage on admission than in those with a good condition and/or mild subarachnoid hemorrhage, in spite of a functional drain. There was a poor outcome in about half of the patients showing maximum daily mean ICP >30 mm Hg or frequent B‐waves. No complications caused by ICP monitoring were found. Because of the relatively less invasive methodology lack of complications, good insight into intracranial conditions and prediction of prognosis, intracranial extradural pressure monitoring was considered to be useful in the management of patients following aneurysmal surgery. (Neurosurgery24:878‐883, 1989)