5-Fluorouracil (5-FU) is the most widely used agent for the management of colorectal cancer. Capecitabine is metabolized by three enzymatic actions, the last of which is mediated by thymidine phosphorylase, to produce 5-FU. Given the oral bioavailability of capecitabine as well as in-vitro and in-vivo findings showing higher expression of thymidine phosphorylase in tumor cells and xenografts compared with normal tissue, capecitabine is an evolving candidate in the management of colorectal cancer with antimetabolite-based therapy. An ideal radiosensitizing agent must balance oncological outcomes with adverse effects and feasibility of administration. This discussion addresses the evolving role of 5-FU in the management of rectal cancer in the neoadjuvant setting in combination with ionizing radiation.