The magnitude of fixation disparity has been proposed to be uncorrelated with stereoscopic sensitivity. Studies on this relationship have been confined to the effects of vergence-induced fixation disparity on stereoacuity: some subjects exhibited decreased stereoacuity with induced fixation disparity. The present study was designed to determine whether prismatic correction of naturally occurring horizontal fixation disparity would result in increased stereoacuity. Five subjects with eso and 5 with exo fixation disparity had their fixation disparity curves and stereothresholds evaluated before and after wearing corrective lenses and prisms that neutralized the fixation disparity. Five subjects with no fixation disparity served as controls. After 1 month most subjects showed no change in their fixation disparity curves and stereothresholds. © 1977 American Academy of Optometry.