Headache in patients with human immunodeficiency virus (HIV) infection may indicate life-threatening illnesses such as opportunistic infections or neoplasms. Alternatively, such patients may develop benign self-limiting headaches. Hence, defining the various types of headache in these patients is essential for proper management. This study describes the clinical characteristics of primary headaches occurring in a group of HIV-infected patients. Of 115 patients seen from 1990 to 1996, 44 (38%) had headaches. Primary headaches were present in 29 (66%) patients and secondary causes were identified in 15 (34%). Among those with primary headaches, migraine occurred in 22 (76%), tension-type headache in 4 (14%), and cluster headache in 3 (10%) patients. Half of those with migraine (n=ll), 1 patient with tension-type headache, and 1 patient with cluster headache developed chronic daily headaches which were severe and refractory to conventional headache or antiretroviral therapy. We conclude that primary headaches in patients with HIV infection are: (1) the commonest type of headache; (2) may present for the first time in individuals with severe immunosuppression; (3) usually bear no relationship to antiretroviral drug therapy; (4) polypharmacy, depression, anxiety, and insomnia are commonly associated comorbidities; (5) frequently do not respond to conventional management and carry a poor prognosis; and (6) do not require neuroradiological and/or cerebrospinal fluid evaluations.