A combination of computed tomography (CT) scanning and volume visualization technology, called virtual colonoscopy (VC) is poised to become the procedure of choice in lieu of the conventional optical colonoscopy for mass screening for colon polyps – the precursor of colorectal cancer. The patient abdomen is imaged by a helical CT scanner during a 40-second single-breath-hold. A 3D model of the colon is then reconstructed from the CT scan by automatically segmenting the colon out of the rest of the abdomen and employing an "electronic cleansing" algorithm for computer-based removal of the residual material. The visualization software, running on a PC, allows the physician to interactively navigate through the colon using volume rendering. An intuitive user interface with customized tools supports 3D measurements, "virtual biopsy" to inspect suspicious regions and "painting" to help in visualizing 100% of the colon surface. Unlike conventional optical colonoscopy, VC is patient friendly, fast, non-invasive, more accurate, cost-effective procedure for mass screening of colon polyps. Our university research of VC led to a license to a Stony Brook, NY company that has installed the technology in numerous sites, thousands of patients have been screened, and the lives of hundreds of patients have been saved. VC has been extended to 3D virtual endoscopy of other organs, such as the heart, arteries, lungs, stomach and bladder. The primary future challenge in VC is in the development of computer-aided detection (CAD) of colonic polyps.