The purpose of this study was to determine and compare the effective dose of multidetector computed tomographic angiography (MDCT) and digital subtraction angiography (DSA) studies for diagnosing a pulmonary embolus (PE). Radiation exposure was measured as computed tomography dose index (MDCT) or as dose-area product (DSA) and was subsequently expressed in the quantity effective dose. Effective doses were obtained in 27 patients who underwent MDCT and in 12 patients who underwent DSA for suspected PE. The MDCT angiography was performed on a Siemens Volume Zoom CT scanner and DSA on a Philips Integris V-3000 system according to standardized protocols. Average effective dose for MDCT angiography of the pulmonary arteries (27 patients) was 4.2 mSv (range 2.2-6.0 mSv). Pulmonary DSA gained an average effective dose (12 patients) of 7.1 mSv (range 3.3-17.3 mSv). Our results show that the effective doses in MDCT angiography studies for PE are moderate and even slightly lower in comparison with pulmonary DSA in a comparable patient group. Variations in patient dose are smaller for MDCT, probably because this procedure can be more strictly protocolized. Patient dose should not be restrictive in the discussion of CTA replacing DSA for diagnosing PE.