Thirty-nine of 225 patients with small cell lung cancer developed brain metastases after the initiation of chemotherapy. Treatment with high-dose dexamethasone in all 39 patients and cranial irradiation in 32 patients resulted in a complete neurological recovery in only eight of 39 patients (20%). Twenty-one of 39 patients (53%) failed to derive lasting benefit from their palliative treatment. Thirteen of 24 patients with limited disease with cranial relapse had no clinical evidence of other distant metastases prior to death and in these patients the CNS disease was an important cause of morbidity. On the basis of this study, it appears that palliative treatment of overt cranial metastases is relatively unsuccessful and that patients with limited disease represent a group with much to gain from effective prophylactic cranial irradiation.