One hundred consecutive headache clinic patients were evaluated prospectively for features of the temporomandibular joint (TMJ) pain-dysfunction syndrome. The syndrome was identified in 14, mainly young women, who differed significantly in physical findings and headache associated symptoms from those with tension or vascular headache, but not in the frequency of anxiety-relieving chronic oral habits usually said to be causal. They resembled tension headache patients in their high incidence of associated depression, and most improved following treatment with physical therapy and tricyclic antidepressants. Radiologic joint abnormalities were uncommon. The TMJ pain-dysfunction syndrome appears to be a frequent, easily diagnosed, and easily treated, but usually unappreciated cause of headache distinct from other headache entities.