We describe 10 new patients and review the 24 prior reports of hemicrania continua, an uncommon, unilateral headache disorder. The disorder is characterized by a continuous baseline headache of moderate severity with superimposed exacerbations of more severe pain. These exacerbations are sometimes associated with ipsilateral autonomic disturbances. There are three temporal patterns: a chronic, nonremitting headache from onset; a remitting variety consisting of distinct phases of continuous unilateral headaches that persist for weeks to months followed by pain-free remissions; and an evolving form in which initially remitting headaches transform into the chronic, non-remitting pattern. Accurate diagnosis is important as all forms are characterized by a dramatic and selective response to indomethacin.