The effective dose equivalent, HE, can be used as a standard radiation dose parameter in all imaging modalities that use ionizing radiation, including positron emission tomography (PET). A simplified method for evaluating approximate HE values for the positron emitters carbon 11, nitrogen 13, oxygen 15 and fluorine 18 is presented. HE values for a range of PET studies have been computed based on biodistribution data available in the scientific literature. Low-dose PET studies include a bolus administration of 1030 MBq CO15O (HE = 1 mSv) and 74 MBq [18F]-L dopa (HE = 1.3 mSv). High-dose PET studies include a 1-h (steady-state) inhalation of a total of 9250 MBq C15OO (HE = 9.4 mSv). The mean HE value of 13 diverse PET studies was computed to be 4.5 mSv.