A 62-year-old Caucasian man with atrial fibrillation who was taking warfarin reported an episode of hematochezia; his international normalized ratio (INR) was 1.74. His weekly warfarin dose was increased by approximately 5%, and he was given three fecal occult blood cards. At follow-up 1 week later, the patient denied any episodes of hematochezia. His INR was 1.69 despite the increased warfarin dosage. One of the occult blood cards showed a positive result, and colonoscopy revealed a 5-cm lesion, identified as Dukes' A adenocarcinoma. Warfarin-associated bleeding generally is considered deleterious; however, in our patient it unmasked an early stage of colon cancer and thus may have saved the patient's life. Although minor gastrointestinal bleeding is common among patients taking anticoagulants, all patients should be fully evaluated because the source of hemorrhage may be malignant.