Introduction: Colorectar carcinoma (CRC) is the third most common cancer site in the World, after breat cancer and lung cancer. According to estimates by the World Health Organization for Cancer Research, almost 2 milion people are diagnosed with it annually, and 0.95 milion die. Colon and colorectal cancer is the most common malignant disease in Croatia. On average, about 3600 people are affected annualy, of which about 60% are men. It is more common in the elderly, but almost 1/5 of patients are younger than 60 years of age. According to the latest dana from Cancer registry, in 2019, 3660 people were diagnosed with colorectal cancer, and the average age at the time of the disease was 69 years. In Croatia, colorectal cancer i sin second place in terms of mortality from malignant diseases, after lung cancer. About 2100 people die from it annualy, and also 60% of men. The five year survival rate of patients with early detection of colorectal cancer is up to 90%, while the 5 year survival of patients with reccurent and metastatic colorectal cancer is less than 12%. According to the latest dana from the Cancer registry, only 11% of colorectal cancer are detected in a localised state, while in 13% of people metastases are alredy present at diagnosis. Patients with colorectal cancer often require perioperative blood transfusions and iron replacement due to anemia, chronic blood loss. There is no general agreement on the effect of blood transfusions on postoperative complications, resurgeries due to dehiscence, length of hospital stay. Aim: The aim of this study was to examine the frequency of perioperative transfusion of erythrocyte concentrate due to anemia in patients with colorectal cancer and to compare the frequency of complications and length of hospital stay between patients who received and did not receive erythrocyte transfusions. Methods: A retrospective study was conducted in a period of 2 years from 2020 to 2021. The study will process the data of 120 patients diagnosed with colorectal cancer who were hospitalized, treated and operated on at the Department of Surgical Oncology, Clinic for Cancer, University Hospital Sister of Mercy . Patients were divided into two groups: the group that received the transfusion of erythrocyte concentrate perioperatively and the group that did not receive transfusions of erythrocyte concentrate. Data to be analyzed: age, gender, surgical method, laboratory findings (complete blood count: helps diagnose various medical conditions, including anemia, infections, etc., CRP-C-reactive protein: a marker in which increased levels indicate the presence of inflammation in the body, SE - erythrocyte sedimentation rate: increased rates indicate the presence of inflammation in the body, PCT - procalcitonin: increased levels of PCT may indicate more severe bacterial infections), perioperative adjuvant treatment, radiotherapy or chemotherapy, in the period from the moment it was decided that the patient should undergo surgery until recovery after surgery when the patient is discharged for home care, the frequency of complications and the length of stay in the hospital. Results: The study included 120 patients (46 women and 74 men) with colorectal adenocarcinoma, with a median age of 69 years. Men were more represented among those younger than 69 years (54%; P = 0.04), and stage 3 of the disease was more common in younger patients (43%; P = 0.04). No significant differences in hospital stay duration were observed by age or gender. Perioperative blood parameters showed a statistically significant decrease in erythrocytes and hemoglobin, along with an increase in inflammatory markers. Older patients had a significant drop in erythrocytes on the 1st and 3rd postoperative days (P < 0.01), while women had lower erythrocyte and hemoglobin levels compared to men before and after surgery (P < 0.01). Conclusion: The study's results confirm that perioperative transfusions significantly impact patient outcomes. Transfusions are associated with longer recovery times and more frequent complications, supporting the hypotheses that patients receiving perioperative erythrocyte transfusions experience more complications and longer hospital stays compared to those who do not. These findings highlight the importance of careful consideration of transfusion indications and the need for further research to optimize transfusion protocols.