['The aim of this study was to evaluate the effect of medication with anticoagulant properties on the false positive rate in a population-based faecal occult blood test (FOBt) colorectal screening programme.', "Eight hundred and forty-six consecutive individuals found to be FOBt-positive in the Scottish arm of the national colorectal cancer screening pilot were studied. All were aged between 50 and 69 years and underwent colonoscopy. Before the procedure the participants' current medication was recorded, and correlated with the colonoscopic findings.", 'Of 846 participants, 301 (35.6%) were taking regular anticoagulant medication at the time of FOB testing. Of these, 143 (47.5%) had colorectal neoplasia found on colonoscopy, whereas of those not taking anticoagulant medication, 308 (56.5%) were found to have neoplasia. This 9% difference was statistically significant (P = 0.012).'] Do medications with anticoagulant properties increase the likelihood of a negative colonoscopy in faecal occult blood test population screening?