Purpose: The aim of this clinical retrospective study was to evaluate the clinical performance and longevity of glass-ceramic onlays and inlays in stress-bearing posterior teeth. Materials and Methods: Five hundred forty-seven posterior teeth in the maxillae and mandibles of 120 patients (46 males, 74 females) were restored with 213 onlays, 38 single-surface inlays, 141 two-surface inlays, and 155 three-surface inlays between 1987 and 2009 at Innsbruck Medical University, Innsbruck, Austria, by two experienced dentists. The restoration sample included 9 (1.6%) nonvital teeth and 40 (33%) patients diagnosed with bruxism. The study population was examined clinically during regularly scheduled maintenance appointments. The risk of failure was determined using Kaplan-Meier survival analyses. Results: The mean observation periods for onlays and all inlays were 80 ± 34 months and 111 ± 63 months, respectively. Twenty-seven failures were recorded. The estimated survival rates for onlays and all inlays after 5, 10, and 12 years were 98.9% and 98.9%, 92.4% and 96.8%, and 92.4% and 89.6%, respectively. Nonvital teeth showed a significantly higher risk of failure (P .001). There was no greater risk of failure associated with existing parafunction (bruxism) (P = .408). Restorations on premolars survived longer in the first 15 years than restorations on molars, but no statistical significance was found (P = .913). Conclusion: Glass-ceramic onlays and inlays were demonstrated to be successful in posterior teeth; however, at this time, their efficacy is inferior to that of cast gold restorations.