Background: The goal of this study is to examine the eff ect of neoadjuvant radiochemotherapy on the density of CD8+ tumor infi ltrating lymphocytes (TILs) in endoscopical bio psies and resection specimens from patients with rectal adenocarcinoma before and after therapy. Patients and Methods: In total, 53 patients with locally advanced rectal cancer were studied. Results: The median density of CD8+ TILs in pretreatment biopsies was 12 (1– 232) and that in surgical specimens after radiochemotherapy was 18 (1– 319). During radiochemotherapy, the density of CD8+ TILs increased in 30 patients (57%), decreased in 18 (34%), and did not change in one. It was not possible to assess the dynamics of CD8+ TILs density in four patients. The increased density of CD8+ TILs after radiochemotherapy was associated with a median survival rate 2.5 times longer than that associated with no increase in density. Conclusion: In the present study, the density of CD8+ TILs in endoscopical bio psies before radiochemotherapy, the density in resection specimens after radiochemotherapy, or in changes in the density after radiochemotherapy showed no predictive or prognostic signifi cance. However, studying a larger number of patients may show that CD8+ TILs density is of predictive or prognostic significance.