PET with (18)F-FDG is a widely used imaging modality in cancer patients. Traditionally, (18)F-FDG is administrated intravenously. However, patients with difficult venous access are not rare in clinical practice. The purpose of the current study was to investigate the dynamic process of (18)F-FDG distribution after oral administration in order to determine the optimal imaging acquisition time in human subjects. On the basis of tissue time-activity curves, we determined the time that was required to reach 90% of the maximal uptake in target organs. In a 50-y-old healthy subject with oral (18)F-FDG administration, we found that (18)F-FDG uptake maximized at 60 min for most organs except for the gray matter of the brain, which continued to accumulate (18)F-FDG after 60 min. Time to 90% was 22 min for liver, 36 min for kidneys, 48 min for myocardium, 50 min for bladder, 56 min for sigmoid colon, and greater than 61 min for gray matter of the brain. We suggest that PET images be acquired at around 60 min after oral (18)F-FDG administration for most organs. For the brain, a longer interval is required before acquisition.