A subarachnoid catheter (SAC) technique of continuous intracranial pressure (ICP) monitoring is presented and compared to intraventricular catheters (IVC's) and subarachnoid bolts (SAB's) in 40 neurosurgical patients. Thirty-one patients were monitored simultaneously with SAC's and IVC's and nine patients with SAC's and SAB's, and the ICP waveforms and measurements were compared. The duration of monitoring ranged from 15 hours to 11 days, and the initial ICP from 2 to 117 torr. A total of 42 SAC's were placed; two that entered brain parenchyma were redirected. One SAC placement was associated with an intracerebral hematoma. There were no infections. For the 31 patients with SAC's and IVC's, there were 2706 pairs of ICP measurements with a mean difference of -0.12 torr and a standard deviation of 5.29 torr. The waveforms from the SAC's and IVC's were indistinguishable. For the nine patients with SAC's and SAB's, there were 773 pairs of ICP measurements with a mean difference of 1.24 torr and a standard deviation of 32.83 torr. The SAB waveforms were of varying quality and all dampened with time. The paired t-test (ts) demonstrated no statistically significant difference between SAC's and IVC's (ts = - 1.19). An analysis of variance demonstrated the scatter of the measurements obtained from SAB's to be 38.5 times that of SAC's, p less than 0.00005. The SAB is shown to be relatively inaccurate with a wide range of variance, while the SAC is demonstrated to be an accurate, reliable, and safe method of continuous ICP measurement and an acceptable alternative to ventriculostomy.