In certain cell culture studies, significant CEA expression was observed in K-ras mutant cells. However, the relationship between high CEA levels and K-ras status has not been sufficiently investigated. In the present study, we aimed to determine the prognostic role of initial CEA and CA 19-9 values in metastatic colorectal cancer patients according to the status of K-ras. Between 2000 and 2010, a total of 215 patients with metastatic colorectal cancer who were treated and followed up in our oncology center were analyzed. Smokers were excluded from the study. The clinicopathological findings and initial CEA and CA19-9 values were determined. K-ras mutation analysis was performed using quantitative PCR evaluation of the DNA from the tumor tissues. Eighty-two patients (38.1 %) were female and 133 (61.9 %) were male, with a median age of 59 years (range 27-83). Based on tumor localization, 127 patients (59 %) were classified as colon cancer patients and 88 patients (41 %) were classified as rectal cancer patients. The majority of patients (83.3 %) had pure adenocarcinoma histology, while 36 cases (16.7 %) had mucinous adenocarcinoma. The initial CEA levels were detected to be high (> 5 ng/mL) in 108 of the patients (50.2 %), while high levels of initial CA 19-9 (> 37 ng/mL) were found in 90 patients (41.8 %). K-ras mutations were detected in 99 of the patients (46 %). K-ras was found to be wild type in 116 patients (54 %). Significant differences were detected between the K-ras wild-type and mutant groups with respect to age and the initial serum CEA levels. Patients with K-ras mutations were younger (p = 0.04) and had higher initial CEA levels (p = 0.02) compared to patients with K-ras wild type. The median overall survival (OS) time and 3-year OS rate for patients with a high initial CEA level (> 5 ng/mL) were significantly shorter than those of patients with a low initial CEA level (< 5 ng/mL) (50.5 months and 61.8 % vs. 78.6 months and 79.1 %, p = 0.014). Furthermore, the patients with low initial CA 19-9 levels (< 37 ng/mL) had a significant better median OS interval and 3-year OS rate (76.1 months and 80.1 %) compared to patients with high initial CA 19-9 levels (> 37 ng/mL) (37.6 months and 55.7 %, p = 0.04). Multivariate analysis indicated that stage at the time of diagnosis (p < 0.001) and low initial serum CEA level (p = 0.037) were independent prognostic factors of OS. For K-ras mutant patients, the stage at diagnosis (p = 0.017), low initial serum CEA level (p = 0.001), and low initial serum CA 19-9 level were found to be independent prognostic indicators of OS. Our findings demonstrate for the first time that the presence of a K-ras mutation correlated with high initial CEA and CA 19-9 levels in patients with metastatic colorectal cancer. Patients with high initial CEA and CA 19-9 levels may potentially predict the presence of a K-ras mutation, and this prediction may guide targeted therapies in these patients.