Background: The FIRIS study (Muro K et al. Lancet Oncol 2010;11:853–860) previously demonstrated the non-inferiority of Irinotecan plus S-1 (IRIS) to FOLFIRI for mCRC, with progression-free survival (PFS) as the primary endpoint. We previously reported that IRIS plus bevacizumab (IRIS/Bev) is very effective as first-line treatment (Komatsu Y et al. Acta Oncol. 2012 May 4). We now report the final results of this study. Methods: Eligible patients had to have mCRC with a confirmed diagnosis of adenocarcinoma, an age of >20 years, ECOG performance status (PS) of 0-1, and no history of prior chemotherapy. S-1 (40-60 mg depending on patients body surface area) was given orally, twice daily for 2 consecutive weeks, and 100 mg/m²irinotecan and 5 mg/kg bevacizumab was given intravenously on day 1 and 15, followed by 2-week rest period, within a 4-week cycle. The primary endpoint was safety. The secondary endpoints included overall response (OR), PFS, and overall survival (OS). Results: A total of 53 patients were enrolled from October 2007 through March 2009. The results were reported for 52 patients with evaluable lesions. The clinical characteristics of the patients were as follows. The median age was 63.5 years (range, 48 to 82). The male:female ratio was 3:2. The most common grade 3 or 4 adverse events were neutropenia (27%) and diarrhea (17%). Grade 3 or 4 hypertension (21%) was attributed to bevacizumab, but there were no life-threatening adverse events, such as gastrointestinal perforation. On an intention-to-treat basis, OR was 63.5% [95% confidence interval (CI) 50.4-76.5%], and the disease control rate was 94.2%. With a median follow-up time of 51.7 months, median PFS was 17.0 months (95%C.I. 14.2-19.8 months) and median survival time was 39.6 months (95%C.I. 34.2-45.0 months). Conclusions: IRIS/Bev is a remarkably active and generally well-tolerated first-line treatment for patients with mCRC. Randomized control trial comparing this regimen with oxaliplatin containing regimen(XELOX or mFOLFOX6 plus bevacizumab: TRICOLORE study) is already started. Clinical trial information: NCT00569790.