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Abstract: 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° pelvic tilt, average cup inclination was 46.2° (32° to 65°; ±7.0°), and average cup anteversion was 19.8° (4° to 37°; ±9.1°). At neutral pelvic tilt, inclination was 44.5° (28° to 59°; ±7.2°), and anteversion was 15.6° (−5° to 33°; ±8.1°). At −10° pelvic tilt, inclination was 42.6° (25° to 61°; ±7.2°), and anteversion was 10.5° (−10° to 37°; ±12.2°). 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. [Copyright &y& Elsevier]