Context: The sentinel lymph nodes (SLNs), as most other regions, are prone to tumoral invasion. In colorectal cancers, they can help the higher levels of pathological examination techniques. Aims: We attempted to investigate the efficiency of the use of radioactive tracer in identifying SLNs in colorectal cancers using the same pathological technique. Settings and Design: This cross‑sectional, single‑center study was carried out from 2014 to august 2016 at Mashhad University of Medical Sciences. Subjects and Methods: The study population included 100 patients with colorectal cancers. We used a radioactive tracer to detect SLNs and to compare the number and involvement of SLNs and non‑SLNs generally and in terms of the tumor site. For pathological study, we used the same conventional method in both the groups. Statistical Analysis Used: Statistical analysis was performed using SPSS 22.0 software (IBM Corp., Armonk, NY, USA) with Chi‑square and Fisher’s exact test, Student’s t‑test, ANOVA test, Mann–Whitney U‑test, and Kruskal–Wallis test. Results: SLNs were detected in 89 of 100 patients. All the remaining 11 patients had T4 lower rectal cancer and the injection was performed ex vivo. We noted ten cases of upstaging due to SLN mapping and nine cases of false negative. Thus, the sensitivity was found to be 43.75%at and the accuracy was 78.65%. Conclusions: We used the same traditional method in both the groups, and our sensitivity, accuracy and upstaging rate were fewer than similar studies. Our recommendation for further studies is to use intensive SLN biopsy method in both groups of SLNs and non‑SLNs. KEY WORDS: Colorectal neoplasms, radioactive tracers, sentinel lymph node biopsy

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