Significant progress has been made in understanding the molecular genetic basis of colorectal cancer (CRC). That information is paving the way to understanding the genetic basis of other tumors, as well. Oncology nurses should anticipate the routine integration of this information and testing of CRC tumors to understand the molecular basis of the disease in clinical practice. Molecular testing can lead to the identification of families at risk for hereditary cancer syndromes, particularly Lynch syndrome, which sometimes is referred to as hereditary nonpolyposis colorectal cancer. Knowledge of the genetic basis of CRC also contributes valuable information aimed at selecting appropriate and effective targeted therapy.