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Background There are a number of reports of polyethylene liner dissociation of third-generation modular acetabular components. This study compares our experience with 2 contemporary systems to determine whether this is an implant- or class-specific problem. Methods This is a single-center retrospective study of 961 primary total hip arthroplasties using 2 third-generation modular cementless acetabular shells: Pinnacle (535) and R3 (426) with a polyethylene liner. Details of all revisions were obtained from local databases and the New Zealand Joint Registry. Kaplan-Meier survival curves were calculated for all-cause revision, acetabular reoperation (including liner exchange), and liner dissociation. Results There were 17 revisions in group 1 (Pinnacle; DePuy Synthes): 17 for recurrent dislocation, 6 for liner dissociations (1.12%), 3 for femoral loosening, and one for deep infection. In group 2 (R3; Smith and Nephew), there were 4 revision procedures: one for infection, 2 for dislocation, and one femoral revision for periprosthetic fracture. There were significantly higher proportions revised in group 1 for all-cause revision, acetabular reoperation, and dissociation (P = .024 to 0.038). The 7-year survival for all-cause revision was 96.1% for Pinnacle and 99.0% for R3 (P = .022), and that in the acetabular reoperation group was 96.9% for Pinnacle and 99.3% for R3 (P = .035). Conclusions There was a higher revision rate for the Pinnacle acetabular component than for the R3 at 7 years. This was mainly due to polyethylene liner dissociation that can occur early or late. It appears to be a problem specific to the Pinnacle cup design rather than a feature of similar third-generation acetabular components.