Fluorine-18 fluorodeoxyglucose positron emission tomography ([18F]FDG-PET) allows in vivo analysis of tissue metabolic activity. Based on the observation that most malignant tumors display a higher metabolic activity than benign tissues, [18F]FDG-PET offers an interesting option for the diagnosis of primary and recurrent malignant tumors. For the oncological surgeon [18F]FDG-PET is particularly helpful for the diagnosis of tumors of the pancreas, colorectum, lung and esophagus. This short review describes the biological basis of [18F]FDG-PET and gives a critical discussion of its role in oncological surgery.