In advanced cancer patients a cell-mediated immunological impairment, both at baseline and during postoperative period, is often found and is associated with poor prognosis. Cortisol is strictly involved in the response to major surgical stress, is an immunosuppressor and causes a redistribution of immunological population cells in different tissues. The aim of the study was to verify serum levels and circadian rhythm of cortisol in patients with colorectal cancer at baseline before surgery and in the postoperative period, and relate it to the immune status. In 21 patients with colorectal cancer undergoing surgery we evaluated the assessment of total lymphocytes, CD4+, cortisolemia, circadian rhythm of cortisol (11 p.m. and 8 a.m.) at baseline and in 3(rd) and 7(th) postoperative days. Increase of cortisolemia, as decrease of total and CD4+ lymphocytes in the postoperative period versus baseline was statistically significant. Patients with an altered circadian rhythm were 47% and 36% at 3rd and 7th postoperative days, respectively. At baseline 19% of patients had an altered cortisol circadian rhythm and it was more frequent in patients with nodal involvement (p<0.05) and with metastasis (p<0.01). No relations between lymphocytopenia and alteration of cortisolemia and cortisol circadian rhythm were found, either at baseline or postoperatively (p<0.05). Lymphocytopenia in cancer patients seems not to be associated with cortisol level and circadian rhythm alteration, either at baseline or after surgical stress. An impairment of circadian rhythm of cortisol was found at baseline in 19% of patients. It was significantly associated with the presence of metastatic disease.