CT colonography (CTC) is increasingly used to detect colonic polyps and cancers, but its impact in practice is also influenced by frequent detection of extracolonic lesions. We have previously documented the frequency and nature of such lesions. The current study was performed to assess the clinical resources and costs associated with the investigation and treatment of extracolonic lesions. We reviewed the reports of 225 consecutive CTC examinations carried out on patients with symptoms of bowel cancer. 116 of the 225 were reported to have one or more extracolonic findings. All 116 patients with an abnormality were followed up for 12-24 months. 24 patients underwent further actions (outpatient attendance, investigations, or surgical procedures) as a result of previously undiagnosed lesions unrelated to bowel cancer. The costs of these further actions were derived from the NHS Reference Costs manual 2004. The total cost for further investigations and interventions was 34,329 pounds sterling and the mean cost over the sample of 225 patients was 153 pounds sterling--more than the cost of the CTC itself. The costs were mainly generated by surgical procedures. Resources consumed as a result of extracolonic findings approximately doubled the costs of diagnostic CTC. These costs, along with inconvenience, anxiety, morbidity and occasionally even mortality suffered by patients, must be offset by the good done to some of those with sub-clinical but potentially lethal diseases.