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Using PET, we measured the whole-body distribution of 11C-(+)-PHNO (11C-(+)-4-propyl-9-hydroxynaphthoxazine), a D2/3 agonist, as a function of time in adult subjects in order to determine the internal radiation dose. Methods: PET whole-body data were acquired after the injection of 11C-(+)-PHNO (∼360 MBq) in 6 healthy subjects (3 male and 3 female). The PET acquisition duration was a maximum of 112.5 min, and 9 discrete time frames were obtained. After reconstruction of the emission data, 6 organs were identified in the images as exhibiting uptake above background levels. Regions of interest were delineated on these organs, and time–activity curves were generated. The time–activity curve data were corrected for the injected activity, specific organ density, and volume, from which normalized accumulated activities (previously known as residence times) were calculated. The normalized accumulated activities were then used with the software code OLINDA/EXM 1.1 to calculate the internal doses for the standard adult male and female models. Results: The mean effective dose was estimated to be 4.5 ± 0.3 μSv/MBq when all subjects were included and the male model was applied for the dosimetry calculation, and the mean effective dose was estimated to be 5.2 ± 0.2 μSv/MBq when the females were considered separately and the female model was applied for the calculation. The organ receiving the highest dose was the liver (17.9 ± 3.9 μSv/MBq), followed by the kidneys (14.3 ± 3.6 μSv/MBq) and the urinary bladder wall (13.5 ± 3.7 μSv/MBq). Conclusion: The estimated radiation doses for 11C-(+)-PHNO are similar to those reported for other radiotracers labeled with 11C. 11C-(+)-PHNO may be used for multiple PET scans in the same subject and remain within regulatory guidelines.