Biplane fluoroscopy is currently used for dynamic, in vivo three-dimensional motion analysis of various joints of the body. The benefits of fluoroscopy compared to conventional optical marker tracking methods are the elimination of marker skin motion artifacts, and the ability to directly quantify in vivo skeletal motion that is not optically accessible while wearing orthotic devices and footwear. One potential drawback for biplane fluoroscopy is the cross-scatter contamination between two gantries, as the acquisitions are typically synchronized to facilitate motion tracking. The purpose of this study was to experimentally measure the magnitude and effects of cross-scatter in biplane fluoroscopic images acquired over a range of gantry angles (45-90°) and kV settings (60-110 kV). Four cylindrical water phantoms of 4, 6, 8, and 10-in diameter were imaged, each containing a 1-in diameter Teflon sphere. The cross-scatter fraction and the relative change in contrast-to-noise ratio due to cross scatter were calculated. Results demonstrated that the crossscatter fraction varied from 0.051 for the 4-in cylinder to 1.326 for the 10-in cylinder at 60 kV, and from 0.010 to 0.832 at 110 kV. The reduction in ΔCNR ranged from 0.974 (110 kV, 75°) for the 4-in cylinder to 0.618 (60 kV, 60°) for the 10-in cylinder. The results suggest that cross-scatter contamination during biplane fluoroscopy is relatively low when imaging distal extremities, and would not likely require antiscatter grids or asynchronous timing circuits. Analyzing joints with more soft tissue may introduce cross scatter that could reduce accuracy and may require additional scatter reduction hardware.