Background: The CellSearch System is a technique to detect circulating tumor cells (CTCs) in patients with cancer. Few data have been published concerning the role of CTCs detection by this method in colorectal cancer. The aim of this study was to correlate the presence of CTCs with the commonest clinical and morphological variables. Patients and methods: Blood samples were collected from 97 patients and 30 healthy volunteers. Quantification of CTCs in 7.5 ml of blood was carried out with the CellSearch System. The results were expressed as number of CTCs/7.5 ml and the cut-off of ≥2 CTCs/7.5 ml was chosen to define the test as positive. Results: Positive CTCs were detected in 34 of 94 patients (36.2%). Correlation was not found among positive CTCs and location of primary tumor, increased carcinoembryonic antigen level, increased lactate dehydrogenase level or grade of differentiation. Only stage correlated with positive CTCs (20.7% in stage II, 24.1% in stage III and 60.7% in stage IV, P = 0.005). Conclusions: CTCs detection by CellSearch is a highly reproducible method that correlates with stage but not with other clinical and morphological variables in patients with colorectal cancer. Colon cancer tumor cells are detectable in all stages. Further studies are warranted.