Introduction: Positron emission tomography (PET) typically provides very little anatomical data, making it difficult to localize regions accurately. Connection between radionuclide and high resolution anatomical imaging (computed tomography – CT) greatly helps with the localization and characterization of the disease. Although CT has several significant benefits, it should be noted that the addition of CT to the PET system has led to a significant increase in the radiation dose. Purpose: The purpose of this research was to evaluate typical doses that patients receive due to CT imaging in standard PET/CT examinations (three protocols) on nuclear medical units in Slovenia and to determine if there were statistically significant differences between them. Methods: We have analysed the patient doses (CTDIvol and DLP) resulting from the CT imaging by three different protocols (protocol 1: PET/CT imaging of the body from the base of the skull to the middle of the femur, protocol 2: PET/CT imaging of the body from the top of the head to the middle of the femur, protocol 3: PET/CT imaging of the whole body) using three different PET/CT machines (at the Department of Nuclear Medicine at the Institute of Oncology - OI, at the Clinic for Nuclear Medicine in Ljubljana – KNM, at the Department of Nuclear Medicine at the University Clinical Center in Maribor – UKC MB). The presented study included 540 patients (weighing between 70 and 90 kg.). With the help of the computer program "Syngo.via" and the patient data archive, we obtained the patients’ weight, height and dose data. Results: The results show the difference in dose between the three NM units in Slovenia when imaging the same body area. For protocol 1, the OI had the lowest average DLP value (260 mGy*cm), KNM had a 10% higher value (287 mGy*cm) and UKC MB 80% higher (470 mGy*cm). Even with protocol 2, OI had the lowest average DLP value (300 mGy*cm), while the KNM had a 23% higher value (371 mGy*cm) and UKC MB 70% higher (520 mGy*cm). Patients who underwent PET/CT imaging at KNM were exposed to the lowest dose in protocol 3 (DLP = 569 mGy*cm), at UKC MB were exposed to 29% higher dose (734 mGy*cm), the highest doses were omitted at OI (766 mGy*cm). Discussion and conclusion: The results show that there are considerable differences in CT contribution to patient doses between the three NM units in Slovenia. This opens the possibility for further optimization of protocols, taking into account technological limitations.