Haziness on coronary angiograms has been interpreted as thrombogenic morphologies such as dissection or thrombus. Haziness is often seen at distal sites following stent deployment. To clarify the pathophysiology of distal haziness of coronary stenting, we performed intravascular ultrasonography (3.5F, 30 MHz) after implantation of 48 Palmaz-Schatz stents in 45 patients. Haziness was defined visually as a reduction in contrast density or an indistinct vessel border. The luminal diameter and videodensitometry score were measured at the distal edge of the stent and distal adjacent segment by quantitative coronary angiography. Luminal diameter and lumen area were measured by intravascular ultrasound. The distal/in-stent ratio was calculated for each measurement to assess the magnitude of the vessel tapering and the reduction in contrast density. Haziness was found in 18 vessels. Qualitative intravascular ultrasound determined dissections (n = 5) and irregular shapes of the lumen compressed by heavy calcium (n = 3) in the hazy vessels. There were no specific morphologies in the other 10 cases. Distal/in-stent ratio of the videodensitometry score was significantly smaller in hazy vessels, but quantitative coronary angiography could not distinguish hazy arteries with dissection or calcium from arteries without specific morphologies. The distal/in-stent ratio of the lumen area (< 0.8) and lumen area at the distal segment (< 5 mm2) were markedly smaller in the 'hazy' group without specific morphologies. Dissection, heavy calcium, and luminal reduction can cause a hazy appearance at the distal stent edge. Quantitative coronary angiography could quantify the haziness, but could not distinguish the morphologies of the vessel wall. Only intravascular ultrasound could assess the pathophysiology of hazy vessels after coronary stenting.