Purpose: To evaluate the outcome of patients with limited-stage small-cell lung cancer (L-SCLC) treated with cisplatin and etoposide (PE), early prophylactic cranial irradiation (PCI), and high-dose twice-daily thoracic radiotherapy (bid RT). Patients and Methods: A total of 76 assessable patients were treated on this phase II trial, which included six cycles of PE. PCI (25 Gy/10 fractions) was delivered during cycle 3 to responding patients. Cycles 4 and 5 included concurrent chemotherapy and thoracic RT (30 Gy/20 bid fractions, a 2-week break, and another 30 Gy/20 bid fractions). Results: Of the 76 assessable patients, 74 patients (97%) suffered grade 3 or greater (3+) toxicity and 61 patients (80%) had grade 4 or greater (4+) toxicity. Of these adverse events, grade 3+ hematologic toxicity occurred in 72 patients (95%), and grade 3+ nonhematologic toxicity occurred in 55 patients (72%). Only one (2%) of the 61 patients who received PCI experienced treatment failure in the brain. The 5-year survival rate of the 76 assessable patients was 24% (median, 20 months). The 5-year survival rate of the 64 patients who received thoracic RT was 29% (median, 22 months). The 5-year cumulative incidence of in-field treatment failure was 34%. Conclusion: This regimen included a high total dose of bid TRT, which resulted in a favorable 5-year survival rate. Local failure remains a problem that will require additional investigation. Newer technology should allow the safe administration of greater doses of RT, which should improve patient outcome. Data from eight trials were combined to demonstrate a relationship between RT dose fractionation and 5-year survival. © 2007 by American Society of Clinical Oncology.