SummaryBackground: Polyunsaturated fatty acids (PUFAs) play a role in the development/progression of colon cancer. The aim of the study was to assess the relation between serum phospholipids PUFAs, colorectal tumour localization and disease progression. Methods: A total of 67 patients (18 with proximal colon, 17 with distal colon and 32 with rectal tumour localization) as well as 16 controls were studied. One year after surgery, 33 patients had disease progression. Serum levels of C16:1(n-7), C18:1(n-9), C18:3(n-3), C20:5(n-3), C22:6(n- 3), C18:2(n-6), C20:2(n-6), C20:4(n-6) fatty acids of se - rum phospholipids were quantitatively measured before surgery by gas-chromatography. Results: Significantly higher mean value of C18:2, as compared to control, has been noted only for patients with proximal (p<0.05) and distal tumour (p<0.03) localization. The lower mean level of C20:5 and unsaturation index (UI) were observed in colorectal cancer patients regardless the tumour localization, but the statistical difference was noted only for patients with proximal tumours (p<0.05, p<0.03). In patients with proximal tumours, significantly lower mean level of C20:4 and UI were noted in patients with disease progression, as compared to patients with proximal tumours without disease progression (p<0.05). Conclusion: The evaluation of PUFAs as a risk/prognostic factor in colorectal cancer patients should take into account tumour localization as a dependent variable.