Background <p>In total hip arthroplasty (THA), correct fixation and positioning of both the acetabular and femoral components are prerequisites for successful outcomes. Continuous registration and analysis of these components from postoperative X-rays is important in quality monitoring after THA. Reliable measurements for positioning assessments are essential in this quality monitoring. The objective of this study was to evaluate the inter- and intra-observer reliability of Mdesk for measuring acetabular component positioning in THA.</p> Methods <p>This was a multicenter inter- and intra-observer reliability study conducted across multiple countries, with 102 patients assessed from 2008 to 2012. Patients with osteoarthritis treated with unilateral total hip arthroplasty (THA) were enrolled in the study. Postoperative AP pelvic and cross-table lateral radiographs were analyzed using the digital image analysis program Mdesk version 4.0. The inter- and intra-tester reliability was assessed by calculating interclass correlation coefficients (ICC) with 95% confidence intervals (CI).</p> Results <p>The intraobserver reproducibility of all measurements was high (ICC &gt; 0.80). The interobserver reliability was high for all measurements (ICC &gt; 0.74), except for Δ lateral offset and cup protrusion, which was only moderate (ICC = 0.665 and ICC = 0.614 and 0.600).</p> Conclusion <p>Mdesk showed high reliability in measuring key acetabular parameters, suggesting it is a viable tool for THA postoperative monitoring.</p>