This review summarizes the result of the distribution studies of 11C-choline (CH) and 2-deoxy-2-[18F]fluoro-D-glucose (FDG) using positron emission tomography (PET) in many patients with various tumors. The procedures were as follows: CH-PET, following transmission scan, emission scan started forty minutes after injection of CH: FDG-PET, following transmission scan, emission scan started forty minutes after injection of FDG. The final images were displayed on a scale of standardized uptake value (SUV). Various tumors were visualized with both CH and FDG. If normal organs took up radioactivity high, however, it was impossible to distinguish the tumor uptake from the normal organ uptake. The following organs showed high uptake: with CH, kidney, liver, pancreas, small intestine juice, and salivary gland; with FDG, brain, heart, and urine. If there was no interference with normal organ uptake, CH-PET visualized tumors as small as 5 mm in diameter, and FDG-PET visualized tumors of 10 mm in diameter. Lung cancer and pulmonary tuberculosis could be differentiated, in many cases, by comparing CH-PET and FDG-PET. In conclusion, CH-PET is very useful for detecting various tumors, particularly if it was combined with FDG-PET. In addition, this review also discusses the rationale for the use of CH-PET for tumor imaging, the dosimetry of CH, and some 18F-substituted choline analogs.