Several studies revealed that expression levels of glutathione peroxidase 1 (Gpx-1) can be associated with cancer development, mainly through its role in hydroperoxide scavenging by regulating intracellular reactive oxygen species (ROS) levels. Therefore, our aim was to investigate the expression of Gpx-1 protein in a population of Polish patients with colon adenocarcinoma in the absence of any therapy prior to radical surgery. The study was carried out using colon tissue from patients with adenocarcinoma of the colon confirmed by histopathological examination. Gpx-1 antibody was used to determine the immunohistochemical expression of Gpx-1. The Chi2test or Chi2Yatesatest were used to analyse the associations between the immunohistochemical expression of Gpx-1 and clinical parameters. The relationship between Gpx-1 expression, and 5-year patient survival was examined using Kaplan–Meier analysis and the log-rank test. Intracellular localisation of Gpx-1 was detected by the use of transmission electron microscopy (TEM). Western blot analysis was used for the evaluation of Gpx-1 protein expression levels in cancer cell lines in vitro. Immunohistochemical study revealed that the high expression of Gpx-1 was associated with the tumour’s histological grade, proliferating cell nuclear antigen (PCNA) immunohistochemical expression, depth of invasion, and angioinvasion (allp< 0.001) (4). The high immunohistochemical expression of Gpx-1 is correlated with poor prognosis of colon adenocarcinoma patients.