The present invention relates to the diagnosis of colorectal cancer. It discloses the use of the protein nicotinamide N-methyltransferase (NNMT) in the diagnosis of colorectal cancer. It relates to a method for diagnosis of colorectal cancer from a liquid sample, derived from an individual by measuring NNMT in said sample. Measurement of NNMT can, e.g., be used in the early detection or diagnosis of colorectal cancer.