There is increasing evidence that the presence of a systemic inflammatory response plays an important role in predicting survival in patients with colorectal cancer. However, it is not clear what components of the systemic inflammatory response best predict survival. The aim of the present study was to compare the prognostic value of an inflammation-based prognostic score (modified Glasgow Prognostic Score (Mgps) 0=C-reactive protein <10 mg l(-1), 1=C-reactive protein >10 mg l(-1), and 2=C-reactive protein >10 mg l(-1) and albumin<35 g l(-1)) with that of components of the white cell count (neutrophils, lymphocytes, monocytes and platelets using standard thresholds) in patients with colorectal cancer. Two patient groups were studied: 149 patients who underwent potentially curative resection for colorectal cancer and 84 patients who had synchronous unresectable liver metastases. In those patients who underwent potentially curative resection the minimum follow-up was 36 months and 20 patients died of their cancer. On multivariate survival analysis only TNM stage (HR 3.75, 95% CI 1.54-9.17, P=0.004), monocyte count (HR 3.79, 95% CI 1.29-11.12, P=0.015) and mGPS (HR 2.21, 95% CI 1.11-4.41, P=0.024) were independently associated with cancer-specific survival. In patients with synchronous unresectable liver metastases the minimum follow-up was 6 months and 71 patients died of their cancer. On multivariate survival analysis only single liver metastasis >5 cm (HR 1.78, 95% CI 0.99-3.21, P=0.054), extra-hepatic disease (HR 2.09, 95% CI 1.05-4.17, P=0.036), chemotherapy treatment (HR 2.40, 95% CI 1.82-3.17, P<0.001) and mGPS (HR 1.44, 95% CI 1.01-2.04, P=0.043) were independently associated with cancer-specific survival. In summary, markers of the systemic inflammatory response are associated with poor outcome in patients with either primary operable or synchronous unresectable colorectal cancer. An acute-phase protein-based prognostic score, the mGPS, appears to be a superior predictor of survival compared with the cellular components of the systemic inflammatory response.