Due to widespread use of screening procedures for colorectal cancer, an increasing number of colorectal malignancies is diagnosed at an early stage. A special subgroup of these patients has polyp carcinoma, which can be diagnosed with histological examination of the removed specimen. In such cases the exact intraoperative localization of the non-palpable lesion is a greater challenge than resection itself. In our case report, radio-labeled colloid was used to identify non-palpable rectal carcinoma after polypectomy in a high risk patient. Using a navigator device, the submucosal injected colloid was detected on the surface of the bowel determining the proper resection level. The proper resection level was double checked with metal clips and by histology. Radio-guided technique may be a preferable method to identify non-palpable colon lesions before surgical treatment.