Objectives: To measure the prevalence, severity, and impact of pain on quality of life for HIV patients; to identify factors associated with undertreatment of pain. Design: Multicentre cross sectional survey. Settings: 34 HIV treatment facilities, including inpatient hospital wards, day hospitals, and ambulatory care clinics, in 13 cities throughout France. Subjects: 315 HIV patients at different stages of the disease. Main outcome measures: Patients: recorded presence and severity of pain and rated quality of life. Doctors: reported disease status, estimate of pain severity, and analgesic treatment ordered. Results: From 30% (17/56) of outpatients to 62% (73/118) of inpatients reported pain due to HIV disease. Pain severity significantly decreased patients' quality of life. Doctors underestimated pain severity in 52% (70/135) of HIV patients reporting pain. Underestimation of pain severity was more likely for patients who reported moderate (odds ratio 24) or severe pain (165) and less likely for patients whose pain source was identified or who were perceived as more depressed. Of the patients reporting moderate or severe pain, 57% (61/107) did not receive any analgesic treatment; only 22% (23/107) received at least weak opioids. Likelihood of analgesic prescription increased when doctors estimated pain to be more severe and regarded patients as sicker. Conclusions: Pain is a common and debilitating symptom of HIV disease which is gravely underestimated and undertreated. Pain is a common and debilitating symptom of HIV disease; it is seriously undertreated This multicentre study shows that pain is present in 62% of HIV inpatients, that its severity decreases their quality of life, and that over half with significant pain do not receive any analgesic treatment Undertreatment of pain in HIV disease is related to doctors both underestimating pain and underprescribing analgesics The more severe the pain, the more often doctors underestimate it Doctors are reluctant to prescribe potent analgesics. Likelihood of analgesic prescription increases when doctors estimate pain to be more severe and regard patients as sicker