A carefully controlled prospective study was made of 66 men aged 17 to 48 with minor head injuries. The mean time off work was 4.7 days, range 0 to 26 days. Time off work was longer: in older patients; after road traffic accidents compared with sports injuries; in patients who had taken alcohol and in 5 who had needed admission to hospital. Post-traumatic amnesia alone did not relate to time off work but was longer in these groups of patients. Sixty per cent of patients had symptoms on return to work and 46 per cent could not do their job as well as usual for a mean time of 14 days. Leisure activities were affected for a similar period and fatigue was common. Ninety days after the accident 20 per cent still had symptoms, mostly defects of memory, concentration and work capacity. Four patients still had symptoms 2 years later. Though describing symptoms, all patients were back at their usual work and non had any claim for compensation outstanding. Major points emerging are the limitations of post-traumatic amnesia as an index of the severity of a minor head injury, and the high incidence of symptoms on return to work and later, in patients who were at work and without compensation claims. The importance is stressed of an effective programme for the management of minor head injuries.