Background: Combination chemotherapy is now considered to be the cornerstone of small cell lung cancer (SCLC). management but the optimal management of limited SCLC is not well defined. The role of thoracic radiotherapy (TRT) is less well established. Recent meta-analyses reports revealed that TRT combined with chemotherapy produce "good" local control and prolonged survival. But other reports that survival was not changed. The timing, dose, volume and fractionation for TRT with the combined chemotherapy of SCLC remains unsettled. In this study, we analyzed the effects according to the timing of thoracic radiotherapy in limited SCLC. Method: All fifty one patients received cytoxan, adriamycin and vincristine(CAV) alternating with etoposide and cisplatin(VPP) every 3 weeks for 6 cycles were randomized prospectively into two groups: concurrent and sequential. 27 patients received 4500cGy in 30 fractions(twice daily 150cGy fractional dose) over 3 weeks to the primary site concurrent with the first cycle of VPP(concurrent gorup). 24 patients received 4000 to 5000cGy over 5 or 6 weeks after completion of sixth cycles of chemotherapy(sequential group). Results: 1. Response rates and response duration: Response rates were not significantly different between two groups(p=0.13). But response duration was superior in the concurrent group(p=0.03). 2. Survival duration was not different between two groups(p=0.33). 3. Local control rate was superior in the concurrent group(p=0.00). 4. Side effects and toxicities: Hematologic toxicides, especially leukopenia, infection and frequency of radiation esophagitis were higher in the concurrent group(p=0.00, 0.03, 0.03). Conclusion: The concurrent use of TRT with chemotherapy failed to improve the survival of limited stage SCLC patients compared with the sequential use of TRT but response duration and local control rate were superior in the concurrent group. Frequency of radiation esophagitis, life threatening hematologic toxicities and infection were more frequent in the concurrent group than sequential group. So, the selection of an optimal schedule of chemotherapy combined with TRT that would lead to a major increase in survival with minimal toxicity is remained to be validated in large scale study in the future.