Thirty-nine hospital outpatients with upper abdominal pain without demonstrable organic abdominal abnormalities and 28 healthy controls were compared blindly with regard to back pain and back abnormalities when subjected to a standardized physical examination of the spine. Seventy-two per cent of the patients versus 17% of the controls were troubled with back pain (P less than 0.001). Seventy-five per cent of the patients with back pain actually had abnormalities revealed at the physical examination, indicating that some organic mechanisms are involved in back pain. Most of the findings were localized to the lower thoracic and thoracolumbar segments, the same segments that innervate the upper gastrointestinal tract. This suggests the existence of a connection between abdominal pain and back pain. Viscerosomatic or somatovisceral reflexes with trigger zones either in the viscera or in the skin, muscles, tendons, or ligaments could be part of the pathophysiology in this syndrome. Fifty-one per cent of the patients had symptoms of irritable bowel syndrome, and 41% had heartburn, which was significantly related to the experience of back pain.