Background: The IDEA international collaboration was established to prospectively combine/analyze data from six randomized trials to assess whether a 3-month course of oxaliplatin/fluoropyrimidines-based adjuvant chemotherapy (CT) is non-inferior to the 6-month current standard treatment in stage III colon cancer (CC). The primary endpoint of IDEA was 3-year disease-free survival. The accrual goal for the French IDEA study was 2,000 patients. Methods: French IDEA randomized patients with stage III CC between 3 months (arm A) and 6 months (arm B) of adjuvant CT with modified (m) FOLFOX6 or XELOX (depending on physician/patient choice). Oxaliplatin was stopped in case of persistent neuropathy grade ≥2 with fluoropyrimidines continuation for the planned duration. Toxicity was graded during treatment and follow-up using NCI-CTCAE v3.0. Results: From May 2009 to May 2014, 2,023 patients were randomized in 129 French centers either to arm A (n=1009, 49.9%) or to arm B (n=1014, 50.1%). 2012 (99.5%) patients had stage III disease (N1: 75%; N2: 25%) and 11 patients had stage II (n=2) or stage IV disease (n=9). Median age was 64 years (18-85). 89.4% of patients received mFOLFOX6, 10.1% of patients received XELOX, and 0.5% of patients did not receive any study treatment. Overall, 94.1% and 77.5% of patients completed 3 months (arm A) and 6 months (arm B) of CT, respectively. Median oxaliplatin dose was 500 mg/m² in arm A and 747 mg/m²in arm B. Toxicity profiles depended on the FU backbone with more grade 3/4 neutropenia on mFOLFOX6 (15.0% vs 6.5%) and more grade 3/4 diarrhea (4.7% vs 8.1%) on XELOX. Grade 2/3-4 peripheral neuropathy was less common in arm A than in arm B (23.2/6% vs 37.9/20.4%). Grade 2/3-4 residual neuropathy for patients with a follow-up of at least 3 years (n=811, median follow-up of 3.91 years) was 2.3/0.5% in arm A vs 3.9/ 2.4% in arm B. At 6 months after randomization, mortality rate was 0.7% (n=7) on arm A and 0.5% (n=5) on arm B. Median follow-up is 2.74 years for the whole population. Conclusions: Both mFOLFOX6 and XELOX were safe. Peripheral neuropathy was lower in arm A than in arm B. Clinical trial information: 2009-010384-16.