18F-fluoride is a positron-emitting bone-seeking agent with favorable pharmacokinetic properties. Its uptake mechanism resembles that of 99mTc-MDP. After IV administration, 18F-fluoride diffuses through the bone capillaries into the bone extracellular fluid (ECF). Its plasma clearance is more rapid than that of 99mTc-MDP and its single-passage extraction efficiency is higher. The fast blood clearance of 18F-fluoride results in a better target- to- background ratio. Bone uptake of 18F-fluoride is two-fold higher than that of 99mTc-MDP. Combining the favorable pharmacokinetic characteristics of 18F-fluoride with the high performance of PET technology, 18F-fluoride is a valuable imaging modality of the skeleton.