['Rectal bleeding is common in the community and in general practice, but few studies have examined the causes of rectal bleeding in patients presenting to general practitioners.', 'To determine the frequency of neoplastic conditions in patients with rectal bleeding presenting in general practice and to explain the associations between presenting symptoms and final diagnoses.', 'We conducted two studies, the first in 1989, the second in 1991, in which we invited Danish general practitioners to register 3-4 patients aged 40 and over presenting with rectal bleeding.', 'In Study 1 among 208 patients aged 40 and over and presenting with a first episode of rectal bleeding, colorectal cancer and polyps were present in 15.4 and 7.7%, respectively. In Study 2 among 209 patients aged 40 and over and presenting with overt rectal bleeding, 156 reported a first bleeding episode or a change in their usual bleeding pattern, and in this group colorectal cancer and polyps were diagnosed in 14.1 and 11.5%, respectively. In the group with unchanged bleeding the cancer polyp prevalence was 6.7% (P < 0.05). The patients in both studies were followed through a yearly letter to the GP for at least 32 and 22 months, respectively.'] Do colorectal cancer and polyps in patients aged 40 years and over who consult a GP with rectal bleeding?