Colorectal cancer (CRC) is one of the most common cancer types in the world. Timely diagnosis of CRC and adenomatous polyps aided by effective screening techniques can considerably reduce mortality from this disease. MicroRNAs constitute a new class of promising biomarkers for a range of human diseases including cancer. The following article assesses the diagnostic significance of miR-146a concentrations in the blood plasma of patients with colorectal cancer. The main group included patients with stages I to III colorectal cancer (n = 102); the control group comprised patients with chronic colitis, nonspecific ulcerative colitis and Crohn’s disease (n = 58) and healthy individuals (n = 42). MicroRNA levels were quantified by reverse-transcription real-time PCR, revealing significantly higher miR-146a concentrations in the samples of patients with CRC than in the controls (p < 0.0001). The optimal diagnostic sensitivity determined by ROC analysis was 47.3 %, specificity was 91.5 %, with AUC = 0.79 ± 0.018. Our findings demonstrate that the studied approach does not have sufficient specificity, but still suggest that miR-146a can be included into screening tests based on quantification of other microRNAs with improved specificity.