Standardized uptake value (SUV) for [F-18]fluorodeoxyglucose (FDG) studies that is commonly used to differentiate malignant from benign tumors and to assess the efficacy of therapy is reviewed as a simplified calculation of the more general modeling approach. Based on such a basis, the merits and limitations of the SUV approach is examined with reference to literature reports on tumor uptake of FDG. Results indicate the complexity and large variation of glucose uptake mechanism in tumors. Consistently performed procedures and more basic studies are needed to improve the utility of FDG SUV.