Background &Aims: We prospectively compared the performance of low-dose multidetector computed tomographic colonography (CTC) without cathartic preparation with that of colonoscopy for the detection of colorectal polyps. Methods: A total of 203 patients underwent low-dose CTC without cathartic preparation followed by colonoscopy. Before CTC, fecal tagging was achieved by adding diatrizoate meglumine and diatrizoate sodium to regular meals. No subtraction of tagged feces was performed. Colonoscopy was performed 3-7 days after CTC. Three readers inte rpreted the CTC examinations separately and independently using a primary 2-dim ensional approach using multiplanar reconstructions and 3-dimensional images for further characterization. Colonoscopy with segmental unblinding was used as reference standard. The sensitivity of CTC was calculated both on a per-polyp and a per-patient basis. For the latter, specificity, positive predictive values,and negative predictive values were also calculated. Results: CTC had an average sensitivity of 95.5% (95% confidence interval [CI], 92.1%-99% ) for the identification of colorectal polyps ≥8 mm. With regard to per-patient analysis, CTC yielded an average sensitivity of 89.9% (95% CI, 86%-93.7% ), an average specificity of 92.2%(95% CI, 89.5%-94.9%), an average positive predictive value of 88%(95% CI, 83.3% -91.5% ), and an average negative predictive value of 93.5%(95%CI, 90.9%-96%). Interobserver agreement was high on a per-polyp basis (κstatistic range,. 61-.74) and high to excellent on a per-patient basis (κstatistic range,. 79-.91). Conclusions: Low-dose multidetector CTC without cathartic preparation compares favorably with colonoscopy for the detection of colorectal polyps. Background & Aims: We prospectively compared the performance of low-dose multidetector computed tomographic colonography (CTC) without cathartic preparation with that of colonoscopy for the detection of colorectal polyps. Methods: A total of 203 patients underwent low-dose CTC without cathartic preparation followed by Colonoscopy. Before CTC, fecal tagging was achieved by adding diatrizoate meglumine and diatrizoate sodium to regular meals. No subtraction of tagged feces was performed. Colonoscopy was performed 3-7 days after CTC. Three readers inte rpreted the CTC examinations separately and independently using a primary 2-dim ensional approach using multiplanar reconstructions and 3-dimensional images for further characterization. Colonoscopy with segmental unblinding was used as reference standard. The sensitivity of CTC was calculated both on a per-polyp and a per-patient basis. For the latter , specificity, positive predictive values, and negative predictive values ​​were also calculat ed. Results: CTC had an average sensitivity of 95.5% (95% confidence interval [CI], 92.1% -99%) for the identification of colorectal polyps> 8 mm. With regard to per-patient analysis, CTC yielded an average sensitivity (95% CI, 86% -93.7%), an average specificity of 92.2% (95% CI, 89.5% -94.9%), an average positive predictive value of 88% (95% CI, 83.3% %), and an average negative predictive value of 93.5% (95% CI, 90.9% -96%). Interobserver agreement was high on a per-polyp basis (κstatistic range, 61-74) and high to excellent on a per-patient basis (κstatistic range, .79-.91). Conclusions: Low-dose multidetector CTC without cathartic for the detection of colorectal polyps.