To elucidate the possible contribution of psychologic factors in the pathogenesis of back pain, an assessment of life events and psychiatric symptoms was undertaken in 80 new referrals. In 57, the back pain had a definite onset recent enough to allow this to be dated accurately; these definite onset cases were divided into 26 in whom a specific organic diagnosis could be made and 31 in whom the cause of the pain was uncertain. An additional 23 patients had chronic pain, or could not date the onset of their symptoms. Unlike previous studies, events that occurred after the onset of back pain and thus could have been a consequence of the back pain were excluded. Before onset of back pain there was a significant excess of adverse life events in those with definite onset back pain of uncertain cause, compared with those with a specific diagnosis: there was no such excess in the periods before referral and attendance at the clinic. Diagnosable psychiatric illness was virtually confined to those with chronic pain. These findings indicate that stress, but not psychiatric illness, is involved in the onset of back pain. Further research is now required to ascertain whether those patients who have many psychiatric symptoms at the time of onset are those who develop chronic pain.