The monitoring of intracranial pressure (ICP) and cerebral perfusion pressure is fundamental to the care of acutely brain-injured patients with altered consciousness. Improving technology should benefit the physician, but it is not known for sure if it benefits the patient. Indications for placement of a monitoring device are discussed. An ICP monitor should be placed in comatose traumatic brain-injured patients with abnormal head computed tomography (CT) or with normal CT and two of the following: age over 40 years, posturing, or hypotension. ICP monitors may be needed in patients with poor-grade aneurysmal subarachnoid hemorrhage, fulminant hepatic failure, and acute bacterial meningitis.