Immediate and delayed traumatic intracerebral hematomas (ICH) can produce devastating secondary brain damage after severe head injury. The relationship between the initial injury and eventual occurrence, size, and time of appearance of such hematomas is not well understood, but has great importance since delayed appearance may necessitate delayed surgical decompression of developing lesions not present on early CT scans. We reviewed the records of 35 consecutive patients with operated post-traumatic ICH to document when these lesions appeared on CT, what were the indications for surgery, and what was eventual outcome. Time between injury and ICH appearance was categorized as immediate (0-3 hours), intermediate (3-6), delayed (6-24) or very delayed (later than 24 hours). ICH appearance was immediate in 20%, intermediate in 6%, delayed in 29%, and very delayed in 46%. Half of the patients were not comatose at the time of admission (GCS greater than or equal to 8). Hematoma removal was prompted by clinical deterioration or failure to improve in half the patients and by uncontrolled intracranial hypertension in the other half. Half the patients died, generally those in traumatic coma immediately after injury although advanced age also was associated with poor outcome. Only about one quarter of patients who require surgical removal of ICH can be shown to have their lesions soon after injury. Most operable intraparenchymal clots develop after initial CT scanning and trauma surgeons must be prepared to recognize and treat this delayed complication of brain injury. Even with aggressive management, ICH contribute significantly to poor outcome and improved treatment must be sought.