Purpose : To compare the images of arterial phase (AP) and portal venous phase (PVP) in the evaluation ofconspicuousness of lesion and peripancreatic arterial and venous opacification in pancreatic diseases. Materialsand Methods : Dual-phase spiral CT was performed in 37 patients with pancreatic adenocarcinoma and 21 patientswith pancreatitis. CT scans were performed with 5mm collimation at 1 : 1 pitch table feed. Images of AP and PVPwere obtained at 30 and 65 seconds after administration of contrast material, was initiated. Using a gradingsystem, images were analalysed for conspicuousness of lesion and vascular opacification(grade 1=good, grade2=fair, grade 3=poor). Results : In pancreatic adenocarcinoma, 35 and 36 of 37 cases showed low attenuation on APand PVP, respectively. With regard to conspicuousness of tumour, PVP(mean grade : 1.24) was superior AP(mean grade: 1.43), but not significantly(p=0.0745). In arterial opacification, AP(mean grade : 1.03) was significantlysuperior to PVP(mean grade : 1.30, ; p=0.0051). In venous opacification, PVP(mean grade : 1.19) was significautlyto AP(mean grade : 2.41 ; p<0.0001). In pancreatitis, 14 and 15 of 21 cases showed localized hypo-attenuatinglesion indicating necrosis or fluid collection, on AP and PVP, respectively. With regard to conspicuousness oflesion, PVP(mean grade : 1.61) was superior to AP(mean grade : 1.81), but not significantly(p=0.1088). In arterialopacification, AP(mean grade : 1.05) was significantly superior to PVP(mean grade: 1.38 ; p=0.0180). In venousopacification, PVP(mean grade : 1.10) was significantly superior to AP(mean grade : 2.33 ; p=0.0005). Conclusion :For the diagnosis and staging of pancreatic disease, dual-phase spiral CT in arterial and portal venous phase maybe recommendable. The portal venous phase of spiral CT seems, however, to be superior to the arterial phasebecause the lesion is more conspicuous and there is venous opacification.