There is a constant drive for radiology departments to acquire newer and improved CT machines in order to facilitate faster procedures and a greater repertoire of examinations. However, it is unclear whether the newer technology provides significantly improved image quality, or carries radiation dose implications for patients during everyday clinical practice. We assessed image quality and radiation dose in 15 children and young adults aged 9.3-19.5 years who underwent thoracic imaging on both 16-slice (16CT) and 64-slice (64CT) CT machines. Images were assessed for image quality on a visual analogue scale (1 = unacceptable; 5 = perfect) and preferred image set. All datasets were diagnostically acceptable (scores of 3 or more). The scores for 64CT datasets were significantly better than for 16CT datasets (mean scores of 4.5 and 4.0, respectively; p<0.05). The mean dose-length product (DLP) given was significantly higher during 16CT examinations at 152 mGy cm (effective dose, 2.1 mSv) than for 64CT examinations at 136 mGy cm (1.9 mSv; p<0.05). On average, 64CT examination DLPs were 16 mGy cm (or 9%) lower than the equivalent 16CT examination DLPs. In the context of childhood and adolescent thoracic CT imaging, and using the same software from the same manufacturers, 64CT examinations provide better image quality and give a lower effective dose than do 16CT examinations. If the choice were available, it would be pertinent to use 64CT for this patient group.