PURPOSE: To measure the effective radiation doses delivered at electron-beam computed tomography (CT) and multi-detector row spiral CT of coronary arteries and to compare these doses with those delivered at catheter coronary angiography. MATERIALS AND METHODS: An anthropomorphic phantom equipped with 66 thermoluminescent dosimeters was imaged at cardiac CT. Four protocols for unenhanced coronary artery calcium scoring were simulated: one with electron-beam CT and three with multi-detector row CT. Four similar protocols for coronary CT angiography were simulated. All multi-detector row spiral CT protocols were performed with retrospective electrocardiographic triggering. Biplane catheter coronary angiography also was simulated. Radiation doses to organs were measured, and effective doses were calculated according to guidelines published in International Commission on Radiological Protection Publication 60. RESULTS: Coronary artery calcium scoring with electron-beam CT yielded effective radiation doses of 1.0 and 1.3 mSv for male and female patients, respectively. The radiation doses at calcium scoring with multi-detector row CT were 1.5-5.2 mSv for male patients and 1,8-6.2 mSv for female patients. Electron-beam CT coronary angiography yielded effective doses of 1.5 and 2.0 mSv for male and female patients, respectively. The highest effective doses were delivered at multi-detector row CT angiography: 6.7-10.9 mSv for male patients and 8.1-13.0 mSv for female patients. Catheter coronary angiography yielded effective doses of 2.1 and 2.5 mSv for male and female patients, respectively. CONCLUSION: Higher radiation doses are delivered at multi-detector row cardiac CT compared with the doses delivered at electron-beam CT and catheter coronary angiography.