Purpose : To demonstrate various artifacts on CT angiography (CTA) and by analysing their frequency and causeto improve diagnostic accuracy and CTA image. Materials and Methods : CTA was performed with spiral CT in 21patients with suspected cerebrovascular diseases. Original spiral CT images were obtained with 120ml nonioniccontrast material, 3.0 ml/sec injection rate, 20-23 sec. Scan delay, 1mm collimation, 2mm/sec table feeds and 1mmreconstruction interval. MIP and SSD images of CTA were reconstructed with editing by using a standard processingalgorithm of volume rendering technique and 3D techniques including Grow, ROI and Paint techniques. Artifacts onCTA were analyzed, and compared with original spiral CT images, conventional angiography and operative results.Results : Artifacts on CTA were classified as follows : arising from CTA reconstruction, spiral CT scanning,physical properties of CT and patient. During CTA reconstruction, background inhomogeneity developed through slabediting(n=21), blurring along the longitudinal axis(n=21), contour artifact(n=21), tapering-off(n=18) and saccularfusion(n=1) developing because of improper threshold and window level, break-off or blurring through missing somesource images(n=13) and incorrect scaling due to computer error(n=2). During spiral CT scanning, stair-stepartifacts(n=21) developed through the effect of by rotation and aliasing, and inhomogeneity(n=21) through profiledecrease. Artifacts related to physical property included those related by the partial volume effect(n=1) and thebeam hardening effect(n=1). Patient- related artifacts included metal artifacts(n=2), caused by a surgical clip,and motion artifacts(n=4). Conclusion : An analysis of the variety, frequency and cause of artifacts on CTA, canlead to better imaging and provide basic information for more exact diagnosis.