Background: CpG island methylator phenotype (CIMP) is characterized by concurrent methylation of multiple CpG islands in tumor DNA, which can inactivate tumor suppressor genes or promote carcinogenesis. The prognostic impact of CIMP on treatment outcome of colon cancer patients receiving adjuvant 5-fluorouracil/leucovorin/oxaliplatin (FOLFOX) is unclear. We investigated CIMP markers in colorectal cancer patients treated with adjuvant FOLFOX. Methods: Sporadic colorectal cancer patients treated with curative resection followed by adjuvant FOLFOX were included. DNA was extracted from formalin-fixed paraffin-embedded surgical specimen. 8 CpG island loci (CACNA1G, CRABP1, IGF2, MLH1, NEUROG1, P16, RUNX3 and SOCS1) were examined using MethyLight analysis. Disease-free survival (DFS) was evaluated according to each methylation loci. Results: A total of 322 patients were included. Methylation at 1 or more loci was observed in 150 patients (46.6%) and 6 or more loci in 15 (4.7%). During a median follow-up duration of 39.7 months, 55 recurrences were observed. Three year DFS in the patient cohort was 84%. CRABP1 (23.9%) was the most frequently methylated loci, followed by p16 (22.7%) and NEUROG1 (20.8%). Patients having methylation at NEUROG1 (3 year DFS 78% in (+) vs. 86% in (-), p = 0.014) and p16 (3 year DFS 78% in (+) vs. 86% in (-), p = 0.12) had worse DFS, whereas methylation at MLH1 had better DFS (3 year DFS 100% in (+) vs. 86% in (-), p = 0.19). In a combined analysis, patients with MLH1(-)/NEUROG1(+)/p16(+) had worst treatment outcome compared to MLH1(-)/NEUROG1(+) or p16(+), MLH1(-)/ NEUROG1(-) /p16(-), and MLH1(+) (3 year DFS 62%, 82%, 87%, and 100%, respectively; p = 0.002). In multivariate analysis, NEUROG1(+)/p16(+) was associated with significantly higher recurrence compared with other patients (adjusted hazard ratio (HR) 2.15 (95% confidence interval (CI) 1.08 - 4.27, p = 0.029). Conclusions: Methylation status of NEUROG1, p16, and MLH1 is associated with recurrence following adjuvant FOLFOX in stage II/III colorectal cancer. Further validation and translational studies to improve treatment outcome in the subset of patients are warranted in the future.