For many types of cancer, 18F-FDG PET/CT is commonly used in evaluation and management, including tumor diagnosis, staging, restaging, treatment monitoring, and radiation therapy planning. Meticulous patient preparation including restrictions of diet and activity and management of blood glucose levels in diabetic patients, as well as an awareness of the effect of medications and environmental conditions, plays an important role toward obtaining good-quality images, which are essential for accurate interpretation. Protocol guidelines for performing PET/CT have been proposed by various societies and groups, including the Society of Nuclear Medicine and Molecular Imaging, the European Association of Nuclear Medicine, the American College of Radiology, and the National Cancer Institute. Standardization of the PET/CT procedure is necessary to enable use of metabolic parameters as imaging biomarkers in routine clinical decision making and to ensure reproducibility and allow comparison examinations across different sites. Though several published articles, including various society guidelines, have addressed the relevant patient preparation variables individually, we believe there is need for further clarification. This article summarizes existing data and proposes a standard patient preparation protocol. © 2014 by the Society of Nuclear Medicine and Molecular Imaging, Inc.