Since first described in 1997, MR colonography (MRC) has since been labelled as a promising new, non-invasive technique for examining the colon. At present time, the examination is ready to be implemented as a supplement to incomplete colonoscopy or preoperative colonic evaluation. Furthermore, MRC seems to have a great potential in the screening for colorectal cancer, since detection of polyps and polypectomy might reduce on the incidence of colorectal cancer. This is speculated in the adenoma-carcinoma sequence theory, which states that most cancers evolve from polyps over a long period and that polypectomy might be curative. Colonoscopy remains the gold standard for full colon evaluation. However, the result of our studies can justify clinical use of MRC on selected indications, e.g. in the cases where colonoscopy is incomplete or technically difficult. Since up to 54% of all preoperative colon evaluations in patients with colorectal cancer and up to 17-23% of regular colonoscopies are incomplete, the clinical potential of MRC is evident. Furthermore, in our studies we have shown the insufficiency of preoperative colonic evaluation by CC. In addition, considering the invasiveness, the serious complications (perforation, bleeding, death) and the lack of patient acceptance in colonoscopy, the need for a safe, patient friendly alternative examination with high sensitivity, is clear. In conclusion, in the three studies that made up this PhD thesis, we have shown: that there are some flaws to the present gold standard of colonic evaluation; that there is an increased morbidity and mortality in the group of patients with missed SC; that patients have a preference for MRC and for fecal tagging compared to CC and bowel purgation and that there is a potential gain in doing preoperative colonic evaluation with MRC on all patients with rectal- or sigmoid colon cancer.