OBJECTIVE Intraarterial papaverine infusions are performed to reverse cerebral arterial vasospasm resulting from subarachnoid hemorrhage, but such infusions may lead to increases in intracranial pressure (ICP). This study was undertaken to determine when ICP monitoring is indicated during papaverine treatment. METHODS Seventy-eight vessels were treated in 51 sessions in 28 patients with symptomatic vasospasm. ICP, papaverine doses, and infusion rates were recorded during treatment sessions. The procedural data, Hunt and Hess scores, Fisher grades, Glasgow Coma Scale scores, and ages for all subjects were reviewed and analyzed retrospectively. RESULTS Baseline ICP ranged from 0 to 34 mm Hg. With typical papaverine doses of 300 mg per territory and infusion times ranging from 5 to 60 minutes per vessel, ICP increases above baseline during papaverine infusion ranged from 0 to 60 mm Hg. Significant (> or = 20 mm Hg) ICP increases during therapy were observed even in patients with low baseline ICP and with papaverine infused at the slowest rate. Patients with a baseline ICP of more than 15 mm Hg were much more likely to have significant ICP increases than were patients with a baseline ICP of 0 to 15 mm Hg. Hunt and Hess scores, Fisher grades, age, and Glasgow Coma Scale scores on admission and immediately before treatment did not correlate with ICP increases during papaverine infusion. Patients with ICP increases of more than 10 mm Hg during therapy were more likely to experience adverse clinical events than were patients with ICP increases of < or = 10 mm Hg. Reduction in the rate of papaverine infusion, or termination of infusion, resulted in reversal of drug-induced ICP elevation. CONCLUSIONS ICP monitoring during intraarterial papaverine infusions for cerebral vasospasm is recommended for all patients and is particularly important for patients with elevated baseline ICP. Continuous ICP monitoring facilitates safe and time-efficient drug delivery.