Positron emission tomography (PET) is a major paradigm shift in medical imaging as it is a molecular modality that images the metabolic activity of tissue. Recently, there has been a major expansion and move from research applications into clinical patient care. The majority of these PET scans are performed to evaluate cancer. Uses include cancer diagnosis, staging, restaging and monitoring response to therapy. There is evolving critical applications of PET in the management of Gastrointestinal (GI) tract malignancies. PET is highly sensitive in the detection of occult GIT tumors, nodal and metastatic involvement to liver and other distant sites, yet the role of CT is essential for anatomical delineation, defining tumor extent and resectability. This manuscript reviews the various indications of PET imaging in GI tract malignancies. This will demonstrate the literature and the wide clinical experiences of PET applications in esophagus, Stomach and colorectal. The primary tumors of abdominal solid organs like pancreas, liver ..etc were beyond the scope of this review. The fundamental role of CT imaging in GI tract malignancies is discussed with more emphasis on the added value of the recent fusion of PET and CT that leads to more precise and expansion of the molecular PET images.