Tumour markers are molecules occurring in blood or tissue that are associated with cancer and whose measurement or identification is useful in patient diagnosis or clinical management. The ideal marker would occur only in patients with malignancy, and would correlate with stage and response to treatment, however, to date there are few reliable prognostic markers in colorectal cancer (CRC), consequently much research is focused on identifying such markers. This review aims to summarise the most important currently available markers in CRC that provide prognostic or predictive information. Amongst others, it covers serum markers such as CEA and CA19-9, markers expressed in tumour tissue such as thymidylate synthase and also the expression/loss of expression of certain oncogenes and tumour suppressor genes such as K-ras and p53. The prognostic value of genomic instability, angiogenesis and proliferative indices such as apoptotic index is discussed.