Computed Tomography (CT) is recognized as a relatively high-dose diagnostic procedure. There is some obscurity in the literature about the doses due to conventional CT, spiral CT and High Resolution Computed Tomography (HRCT) of the chest. Conventional chest CT results in a radiation dose approximately 100 times that of a standard chest film and 10 times that of a mammography; on the other hand, conventional chest CT is safe for the lens and the pelvis (ovaries, testes and uterus). Radiation dose associated with helical CT is potentially lower than the dose associated with conventional CT. HRCT, consisting of 1- to 2- mm thick-sections performed at 10 mm intervals, has an effective radiation dose lower than that of conventional CT, even with high-dose techniques (400 mAs). HRCT scans obtained at reduced milliamperage (40-80 mAs), the so-called "low-dose HRCT technique", may provide satisfactory visualization of lung parenchyma in the majority of cases and is recommended in patients in whom radiation dose is a major concern (pediatric population or young women in order to minimize breast irradiation). The awareness of radiation dose will become increasingly important for both referring physicians and radiologists when determining indications and deciding which types of imaging procedures and specific protocols should be used.