The addition of radiotherapy to combination chemotherapy has been shown to improve survival for patients with limited small cell lung cancer (SCLC). Although SCLC is very sensitive to radiotherapy, the impact of radiation may be confounded by interaction among various radiotherapy factors or by the chemotherapeutic agents used in combination. The potential effects of such radiation factors as dose, volume, fractionation, sequence with chemotherapy, and timing (early v late), as well as choice of chemotherapy, therefore must be carefully considered when designing or comparing clinical trials of combined modality therapy for SCLC. The combination of thoracic radiotherapy plus platinum-based chemotherapy currently represents the cornerstone of such combination treatment for SCLC. Many questions remain, however, and it is hoped that new trials will be designed to focus more precisely on unsettled issues.