Vertical acetabular implant positioning is an important technical aspect in total hip arthroplasty. To evaluate the potential benefit of an inclinometer, 50 cup insertions were done on a cadaver pelvis. Acetabular cup vertical angles averaged 44.4 o +/- 11.4 o by visuospatial perception and 42.2 o +/- 3.8 o with the inclinometer. All cups were within the safe angle range of 40 o to 49 o with the inclinometer compared with 64% of cups by visuospatial perception. Use of the inclinometer reduced variability by a factor of 2.0 to 4.5. The addition of an inclinometer for acetabular cup insertion increases the probability of positioning the cup within a vertical safe range during total hip arthroplasty on a cadaver pelvis, suggesting that it could be a useful adjunct in clinical practice.