Background: The aim of our study was to evaluate the prognostic role of various circulating cell-free DNA (cfDNA) parameters in metastatic colorectal cancer (mCRC) patients. Methods: We used a novel method, termed Intplex, which determines simultaneously from plasma, total cfDNA concentration, cfDNA fragmentation level, KRAS/BRAF mutational status, and cfDNA mutation load (% of mutant cfDNA). These parameters were tested in a mCRC patient cohort (n=98), which enabled validation of plasma DNA as a liquid biopsy to detect KRAS/BRAF mutations using the STARD criteria . Results: Median overall survival (OS) of the patients of the full cohort was 22 months (IC 95% [16.9-28.1]). Data confirmed BRAF mutational status as an excellent factor of poor prognosis (median OS, 22.9 vs. 3.4 months; relative risk (RR)=8.9, (IC95% [3.1-25.4], P<0.001) compared to KRAS mutational status (RR=1.1, IC 95% [0.7-1.9], P=0.66). OS was statistically different in patient groups with lower total cfDNA concentrations (median=28.1 months) compared with those with higher total cfDNA concentrations (median=17.8 months) than the median (RR=1.94, IC 95% [1.2-3.2], P=0.009). By using the multivariate Cox model, total cfDNA conc. proved statistically to be a strong, independent prognostic factor (P=0.035). Median OS was 31.1 and 11.1 months (P=0.121; RR=1.8, IC 95% [0.9-3.8]) in patients with lower and higher mutation loads than the median (10.3%). This difference was confirmed statistically when considering the mutant cfDNA conc. median (i.e. 3.1 ng/ml, RR=2.4, P=0.015). The fragmentation level did not appear to discriminate patients with regards to survival. CEA level at the conventional threshold conc. (5 ng/ml) was as a moderate prognostic factor (OS, 27.1 vs. 21.8 months; RR=1.24, 95% IC [0.7-2.2], P=0.48). Conclusions: Our study demonstrates for the time in a large cohort of mCRC patients that in addition to providing an advantageous alternative to tumor-tissue analysis for point mutation detection, other cfDNA parameters, such as total conc. and mutation load, are strong prognostic factors. Thus, prospective studies are needed to confirm multi-marker cfDNA analysis as a simple tool to help define the best care management options.