To improve the efficacy of a combination of cisplatin and etoposide and concurrent accelerated twice-daily thoracic radiotherapy against limited-stage small-cell lung cancer, we conducted a phase I/II study using an altered schedule of chemotherapy administration. Chemotherapy consisted of four cycles of cisplatin (days 1 and 8) and etoposide (days 1, 2, 8, and 9) every 4 weeks. Accelerated hyperfractionated thoracic radiation (1.5 Gy twice daily x 30 fractions, total dose of 45 Gy) was concurrently given with the first cycle of chemotherapy. The recommended doses of cisplatin and etoposide determined in the phase I study were 40 and 80 mg/m(2), respectively. In the phase II study, the overall response rate was 100% (complete response: 32%, partial response: 68%). By a median follow-up time of 29 months, median radiation-outfield progression-free survival was 13.4 months, while radiation-infield progression-free survival did not reach median value. The median overall survival time was 22.9 months, with survival rate of 48.4% at 2 years. Major toxicities were leukopenia and neutropenia (>/=grade 3, 92% each). The local control and overall survival demonstrated in this study were excellent. However, the insufficient distant control suggests a need for development of more active chemotherapy regimens.