Background: Esophagectomy (E) is the standard of care for stage I esophageal squamous cell carcinoma (ESCC), while chemoradiotherapy (CRT) is a treatment option. A parallel-group controlled trial including randomized arms to confirm the non-inferiority of CRT to E for stage IA ESCC was conducted. Methods: Patients (pts) with thoracic ESCC, adenosquamous cell, or basaloid cell carcinoma with stage IA (T1bN0M0), age 20 to 75, performance status 0 to 1, and adequate organ function were eligible. If pts accepted randomization, they were randomly allocated to E with 2-3 field lymph node dissection (arm A) or CRT (arm B). However, if pts had a preference and refused randomization, they were allocated to pts preference arm, E (arm C) or CRT (arm D). CRT consisted of cisplatin and 5-FU, with radiation at the dose of 60 Gy concurrently. The primary endpoint was overall survival (OS) of arm A and B, secondary endpoint included OS of arm C and D using inverse probability weighting with propensity score. The planned sample size in arm A and B was 114 pts in total with one-sided alpha of 10%, power of 75% and non-inferiority margin of HR as 1.78. The sample size in arm C and D was at least 156 pts in each arm with one-sided alpha of 2.5%, power of 85% and non-inferiority margin of HR as 1.78. Results: Between December 2006 and February 2013, 379 (Arm A: 4, B: 7, C: 209 C, D: 159) pts were enrolled. Primary endpoint was not calculated due to small number of randomized arms. Patients characteristics of arm C and D were as follows; median age: 62 and 65, male (%): 82.8 and 88.1, PS 0 (%): 99.5 and D 98.1. All histologic type was SCC except one basaloid cell carcinoma in arm C. The 3- and 5-year OS were 94.7% and 86.5% in arm C, and 93.1% and 85.5% in arm D (adjusted HR 1.05; 95% CI 0.67-1.64 [< 1.78]).Treatment related death were observed in two pts in arm C and none in arm D. Conclusions: Though the accrual of randomized arms was shortened, CRT showed trend toward non-inferiority compared to E in pts preference arms. CRT is considered as a treatment option for stage IA ESCC with organ preservation. Clinical trial information: UMIN000000551.