Headaches due to insufficient or interrupted sleep are generally labelled "tension headaches" of psychogenic origin. In 25 healthy subjects, variable amounts of sleep loss (1-3 h for 1-3 nights) caused headaches lasting from 1 h to all day. The headache was most frequently a dull ache, a heaviness or a pressure sensation felt in the forehead and/or at the vertex. Simple analgesics, purchaseable without a doctor's prescription, completely or markedly reduced the head pain in 20-60 min. Headaches due to insufficient sleep differ from tension headaches in their site, duration and response to analgesics. Assuming that pain implies a regional dysfunction, headaches caused by sleep loss provide support for the notion that sleep has a restorative function in the brain.