We have consecutively studied 110 patients with traumatic subarachnoid hemorrhage (tSAH) on the first Computed Tomography (CT) scan (obtained in each case within 3 hours from injury). The only exclusion criteria were brain death on admission, and severe hypotension due to extracranial injuries. All CTs were reviewed by one of us and the "worst" CT examination was determined. We defined the worst CT examination as that showing the most extensive degree of parenchymal-associated damage. Intracranial pressure was monitored in 25 severely head injured patients. Seventy-four patients (66%) showed an evolution from the initial CT scan (worst CT not corresponding to the admission CT). The outcome was favorable in 53 cases (73%) of patients with evolving lesions and in 32 cases (89%) with non evolving lesion. In the 25 severely head injured patients, Intra-cranial Pressure (ICP) monitoring (in combination with scheduled repeat CT scan) was helpful to identify the timing of the worst parenchymal damage and of surgery in those patients with an initial normal intracranial pressure in spite of an evolving lesion.