To describe the treatment of cancer pain in France and to evaluate the predictive factors for inadequate management. Multicentre, representative cross sectional survey. 20 treatment centres, including cancer centres, university hospitals, state hospitals, private clinics, and one homecare setting (in which patients are supported at home). 605 patients with cancer. Patients rated prevalence and severity of pain and functional impairment related to pain. Doctors reported patients' cancer characteristic, performance status, pain severity, and analgesic drugs ordered. 57% (340/601) of patients with cancer reported pain due to their disease, and, of those with pain, 69% (224/325) rated their worst pain at a level that impaired their ability to function. 30% (84/279) were reported as receiving no drugs for their pain. Of the 270 patients in pain for whom information on treatment was available 51% (137/270) were not receiving adequate pain relief, according to an index based on the World Health Organisation's guidelines. French doctors were found to underestimate the severity of their patients' pain. Younger patients, patients without metastatic disease, patients with a better performance status, and patients who rated their pain as more severe than their doctors did were at greater risk for undertreatment of their pain. In the light of the high prevalence and the severity of pain among patients with cancer, the assessment and treatment of cancer pain in France remain inadequate, emphasising the need for changes in patient care.