Purpose: To examine the effect of changing the experimental scatter condition on densitometric stenosis measurements. Methods: Experiments were conducted using an experimental digital fluoroscopic system. A test phantom with a known degree of stenosis was imaged before and after the introduction of an iodine-based contrast medium to simulate the digital sub traction angiography (DSA) process. The scatter to primary ratio has been reported to be affected by area irradiated, thickness of the part, kVp, and use of scatter reduction methods such as grids and airgaps. Each of these conditions were manipulated experimentally with densitometric stenosis measurements determined for each scatter condition. Results: Theoretically and experimentally, it is shown that the densitometric analysis produces a grossly inaccurate measurement of the degree of vessel stenosis when performed on images acquired under scatter conditions. (C) 2000 The College of Radiographers.