OCCUPATIONAL APPLICATIONS Occupational sitting has been associated with an increased risk for developing low back pain. The present investigation examined the effects of asymmetrical sitting surfaces induced by a wallet on acute changes in spine/pelvis posture, interface pressure, and discomfort. Compared to level sitting, sitting on a wallet resulted in greater sagittal and lateral spine flexion, a smaller total contact area with the seat pan, and greater gluteal discomfort. At wallet thicknesses of 22 mm and thicker, seat pan contact pressure area decreased and thoracic spine and pelvic angles deviated laterally compared to the no-wallet condition. At a 32-mm wallet thickness, gluteal discomfort increased. These results indicate that sitting for brief periods (15 minutes) on an uneven seating surface greater than 32 mm in thickness causes postural deviations from neutral spine positions and increases gluteal discomfort. This study supports the removal of rear pocket items, especially larger ones, during sitting.