To test the hypothesis that Spiral Computed Tomography (SCT) may both replace pulmonary Digital Subtraction Angiography (DSA) in the diagnosis of acute pulmonary embolism (PE) and serve for follow-up evaluation of PE after thrombolytic therapy contrast enhanced SCT and DSA were performed pros pectively in 50 patients. Sixteen patients underwent follow-up SCT after thrombolysis. Axial images, 3-D-shaded surface displays (SSD) and maximum intensity projections (MIP) obtained from SCT-data were compared with DSA-results by two blinded observers. Both methods were evaluated for quality of vascular contrast and detection of intraluminal clots or filling defects.38 patients showed evidence of PE in SCT and DSA. All 12 patients with normal findings on SCT had normal findings by DSA. Vascular contrast was graded excellent in 66% of SCT-but only 32% of DSA examinations. SCT detected 217 thrombi in central (n=22), lobar (n=100)- and segmental pulmonary arteries (n=95) as compared to a total of 187 thrombi by DSA (central n =22, lobar n =92, segmental n=73); the 30 thrombi identified only by SCT revealed partial filling defects (unseen by DSA) rather than false positive findings. After thrombolysis 56/135 initial thrombi did not resolve completely at F/U according to SCT. SCT with SSD and MIP were time consuming and did not increase diagnostic input to SCT results.SCT is a promising noninvasive alternative to DSA in the diagnosis of PE and for follow-up evaluation after pulmonary thrombolysis and may emerge as a new diagnostic standard.