 Screening for colorectal cancer is now being introduced in many countries worldwide, but there is still considerable uncertainty as to the ideal modality. Population based trials of guaiac faecal occult blood testing gFOBT have consistently demonstrated significant reductions in disease specific mortalities and three randomised population based trials of biennial gFOBT have demonstrated reductions in deaths from colorectal cancer of around 16. As a result of these trials, a demonstration pilot was performed in the United Kingdom which has led to the introduction of gFOBT screening in all four countries of the United Kingdom. 