Colorectal cancer is a major cause of morbidity and mortality accounting for an estimated 550,000 deaths annually worldwide. Colonic neoplasia develops in a stepwise fashion progressing from normal mucosa to adenomatous polyps to carcinoma, a process that takes years, thereby providing a prime opportunity for intervention. Although early detection by fecal occult blood testing and sigmoidoscopy can decrease the risk of cancer-related death by 20-30%, most persons never undergo appropriate screening. Population-based studies have previously determined that long-term ingestion of aspirin or other nonsteroidal antiinflammatory drugs (NSAIDs) leads to a 40-50% reduction in mortality. from colorectal cancer. These observational studies fueled subsequent mechanistic investigations that led to the identification of a molecular target, cyclooxygenase-2 (COX-2). COX-2 has tumor-promoting properties. Expression of COX-2 is virtually undetectable in normal intestinal mucosa, but is increased in approximately 50% of colonic adenomas and in 90% of colorectal carcinomas. Experimental studies in mice have revealed that genetic ablation or pharmacologic inhibition of COX-2 attenuates the number and size of intestinal polyps that develop in animals harboring a mutation in Apc, which confers an increased risk for intestinal neoplasia. Recent clinical studies using specific COX-2 inhibitors have shown that these compounds can: (1) reduce intestinal polyp burden in patients with familial adenomatous polyposis; (2) prevent the occurrence and/ or recurrence of colorectal adenomas and cancers; and (3) negatively regulate angiogenesis in colorectal cancer liver metastases. Compared to nonselective NSAIDs, COX-2 specific inhibitors cause substantially fewer gastrointestinal side effects. These findings indicate that a widely used and relatively safe class of drugs may represent a viable and effective anticancer strategy for a disease that causes over a half-million deaths per year.