A prospective study of 3000 consecutive patients with head injury admitted to hospital showed a marked seasonal, daily and hourly variation and an overall male-to-female ratio of 2.19:1. The majority of patients were in the second, third and fourth decades of life with a peak in the early part of the second decade. The incidence was highest in unemployed and welfare recipients. Traffic accidents were the leading cause followed by fights and falls. Drug or alcohol use, or both, was evident in 45.6% of cases. The number of head injuries caused by intoxicated individuals is not known. Most patients had a concussion only. There was no evidence that the patients with concussion who returned to full activity immediately had any more adverse effects than those advised to "take it easy" for about 1 week.