High intracranial pressure (HICP) may be a very early event after traumatic brain injury (TBI), but in most cases, especially when contusions and edema develop over time, HICP will worsen over succeeding days. This study describes the incidence and severity of elevated intracranial pressure (ICP) after TBI and attempts to document its time course. In this prospective study, 201 TBI patients in whom ICP was monitored for more than 12 h were evaluated. ICP was measured, digitalized, and analyzed after manual filtering. The number of episodes of HICP and the mean ICP value for every 12-h interval were calculated. When monitoring was concluded, the highest mean ICP collected in every patient was identified. A total of 21,000 h of ICP monitoring were recorded. Active treatment to prevent or reduce HICP was used in 200 patients. HICP was documented in 155 cases. Half of the patients had their highest mean ICP during the first 3 days after injury, but many showed delayed ICP elevation, with 25% showing highest mean ICP after day 5. In these cases, HICP was significantly worse and required more intense therapies.