OBJECTIVE The study objective was to evaluate the efficacy and toxicity of chemoradiotherapy with 5-fluorouracil (5-FU) plus cisplatin in patients with Stage I esophageal squamous cell carcinoma (ESCC). The primary endpoint was proportion of complete response (%CR). METHODS Patients with Stage I (T1N0M0) ESCC, aged 20-75 years, without indication of endoscopic mucosal resection were eligible. Treatment consisted of cisplatin 70 mg/m(2) (day 1) and 5-FU 700 mg/m(2)/day (days 1-4) combined with 30 Gy radiotherapy (2 Gy/day, 5 days/week, days 1-21). The cycle was repeated twice with 1-week split. Salvage surgery was recommended for residual tumor or local recurrence. RESULTS From December 1997 to June 2000, 72 patients were enrolled. No ineligible patient or major protocol violation was observed. There were 63 CRs for %CR of 87.5% [95% confidence interval (CI): 77.6-94.1]. Six patients with residual tumor successfully underwent esophagectomy. There was no Grade 4 toxicity. Four-year survival proportion was 80.5% (95% CI: 71.3-89.7), and 4-year major relapse-free survival proportion was 68% (95% CI: 57.3-78.8) (mucosal recurrence removed by endoscopy was not counted as an event). CONCLUSIONS High CR proportion and survival proportion with mild toxicity suggest that this regimen could be considered as a candidate of new standard treatment to be compared with surgery in patients with Stage I ESCC.