Chest pain is often a major problem in patients with malignant pleural mesothelioma but there are few data regarding the usefulness of radiotherapy (RT) in its palliation. Following a recent retrospective report which suggested that wide-field RT frequently affords pain relief in this disease, we prospectively assessed the effect of hemithorax irradiation on pain control. Twenty-two patients with chest pain due to mesothelioma received 30 Gy in 10 daily fractions to the involved hemithorax. The patients' symptoms were assessed before RT, 1 month after RT, and then 2 monthly. Symptoms were graded by the clinician and the patient, and analgesic requirements were noted at each assessment. Performance status and respiratory status were recorded by WHO and MRC criteria respectively. Nineteen assessable patients have been followed for at least 3 months after RT. The treatment was well tolerated, with nausea and vomiting in only 1 patient. Pain control improved in 13/19 patients at 1 month, but 9/12 patients had worsening chest pain at 3 months, and at 5 months pain control had deteriorated in 6/7 patients. Although partial regression of chest wall masses was seen in 5/9 patients, RT did not appear to delay the progression of respiratory symptoms or radiological changes. The median duration of survival after RT was 4 months. Radiotherapy can relieve pain due to malignant pleural mesothelioma but its effect at this dose is short-lived.