Primary traumatic brain damage may be compounded by secondary pathophysiological insults that can occur soon after trauma, during transfer to hospital or subsequent treatment of the head-injured patient. The aim of this prospective study was to quantify the burden of a wide range of secondary insults occurring after head injury and to relate these to 12-month outcome. In 124 adult head-injured patients studied during intensive care using a computerized data collection system, < or = 14 clinically indicated physiological variables were measured minute-by-minute. Verified values falling outside threshold limits for > or = 5 min, as defined by the Edinburgh University Secondary Insult Grading scheme, were analysed by insult grade and duration. A greater incidence of secondary insults was detected than previous studies have indicated. Insults were found in 91% of patients and occurred in all severities of head trauma, at all ages, and at every level of Injury Severity Score (ISS). The cumulative durations were much greater than previously recorded although 85% of the total time was at the least severe grade. Short duration insults were common. In 71 patients, in whom 8 insults could be assessed (intracranial pressure, arterial hypo- and hypertension, cerebral perfusion pressure, hypoxemia, pyrexia, brady- and tachycardia), outcome at 12 months was analysed using logistic regression to determine the relative influence of age, admission Glasgow Coma Sumscore, ISS, pupil response on admission, and insult duration on both mortality and morbidity. The most significant predictors of mortality in this patient set were durations of hypotensive (p = .0064), pyrexic (p = .0137), and hypoxemic (p = .0244) insults. When good versus poor outcome was considered, hypotensive insults (p = .0118) and pupil response on admission (p = .0226) were significant.