Justification of medical exposures, especially of the high dose CT exams, should be fully implemented. The purpose of this study was the investigation of the unjustified CT head and abdomen exams and the evaluation of patient doses in a tertiary Greek hospital.Two radiologists reviewed and evaluated the justification of 209 CT Head and 283 CT Abdomen referrals based on the American College of Radiation Appropriateness Criteria® and medical expertise. Patient status (emergency or not) and diagnostic outcome (positive/negative) were recorded. Effective doses were calculated based on Dose-Length-Product indications.Sixty (29%) of the Head examinations were considered unjustified and could have been replaced by MRI or not a radiological examination was needed, referred mainly for minor head trauma and headache. Sixty-eight (24%) of the Abdomen examinations were considered unjustified and could have been replaced by MRI &/ US or other type of examination, referred mainly for malignancy screening and abdominal pain. Thirty-seven of the Head and 37 of the Abdomen unjustified exams had negative outcome. The odds of having negative outcome for the unjustified exams compared with the justified ones were twofold (p < 0.0001). More unjustified examinations were referred for the non-emergency patients (p < 0.0001). Collective dose was 10.1 manSv for the Head exams of which 1.7 manSv were unjustified and negative and 71.4 manSv for the Abdomen exams of which 9.4 manSv were unjustified and negative.The non-implementation of referral criteria by clinicians for CT Head and Abdomen exams leads to a nearly 14% of unnecessary patient doses.