The emerging techniques of 3D spiral CT for 'virtual colonoscopy' show promise as a noninvasive screening modality for the detection of polyps. Our purpose was to evaluate three key post-processing parameters required for depiction of colonic polyps using perspective volume rendering (PVR): image reconstruction, window setting, and opacity map assignment of the attenuation histogram. Spiral CT scans of two different patients with known polyps confirmed by colonoscopy were performed. First, image quality was compared between images generated after interpolation of raw projection data and interpolation of reconstructed image data for longitudinal voxel dimensions of 1x, 2x, 4x, 6x and 8x in-plane voxel dimensions. Second, the dimensions of colonic polyps relative to haustral folds were measured on PVR images for various window settings and compared to similar measures performed on photography performed at colonoscopy. Third, a double sigmoidal and a stair-step opacity function were each applied to a 3D PVR image of a polyp, and quantitative differences in image smoothness were compared using a texture analysis method. In conclusion, spiral CT images reconstructed with 50 percent overlap and displayed with a standard display window permit accurate depiction of polyp dimensions relative to surrounding structures on PVR windows. Image artifacts may be suppressed with use of a double sigmoidal opacity map.