Background: The existence of air in hollow organs in the thoracic cavity constitutes a life-threatening situation most of the times. However, sometimes in thoracic Computed Tomography (CT) there are artifacts from different sources that could mimic air densities, disorientating the diagnosis. Materials and Methods: 100 patients (46 females and 54 males, mean age: 60 years, range: 20-90 years), who had been routinely scanned in the area of thorax using three different imaging protocols (follow up, aorta, pulmonary vessels) were retrospectively studied. In 67 cases, contrast agent was used during the examination. Every case was studied by two specialists. Results: Artifacts in pulmonary veins were observed in 38 of the cases. Of these artifacts 27 stemmed from contrast agent, calcifications in the vessels, metallic implants, movement of the patient, malfunction of a detector due to the size of field of view (FOV) or due to the existence of contrast agent on the examination table of the CT scanner. In 11 cases, small amounts of air had been inserted into blood circulation during contrast injection. Conclusions: This study characterized and classified many artifacts related to thorax CT in order to separate them from other serious thoracic pathologies (e.g. aortic dissection, ulcer of veins or arteries). The knowledge and identification of the different types of artifacts is very important in order to avoid the risk of misdiagnosis.