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This study investigates the influence of pelvic tilt on conventional alignment of acetabular cups. Cementless cups were aligned into a synthetic replica of the pelvis 300 times at different pelvic tilts. At +10 degrees pelvic tilt, average cup inclination was 46.2 degrees (32 degrees to 65 degrees ; +/-7.0 degrees ), and average cup anteversion was 19.8 degrees (4 degrees to 37 degrees ; +/-9.1 degrees ). At neutral pelvic tilt, inclination was 44.5 degrees (28 degrees to 59 degrees ; +/-7.2 degrees ), and anteversion was 15.6 degrees (-5 degrees to 33 degrees ; +/-8.1 degrees ). At -10 degrees pelvic tilt, inclination was 42.6 degrees (25 degrees to 61 degrees ; +/-7.2 degrees ), and anteversion was 10.5 degrees (-10 degrees to 37 degrees ; +/-12.2 degrees ). Overall, 50% of the cups were positioned outside the safe zone: 46% in pelvic inclination, 42% in neutral position, and 63% in pelvic reclination (P = .007). This study shows the considerable inaccuracies of conventional cup implantation by experienced and trainee surgeons and shows the influence of pelvic tilt on acetabular cup alignment.