Purpose: This study aimed to investigate the clinical outcome and estimated cumulative survival rate of feldspathic porcelain veneers in situ for up to 21 years while also accounting for clustered outcomes. Materials and Methods: Porcelain veneers (n = 499) placed in patients (n = 155) by a single prosthodontist between 1990 and 2010 were sequentially included, with 239 veneers (88 patients) placed before 2001 and 260 veneers (67 patients) placed thereafter. Nonvital teeth, molar teeth, or teeth with an unfavorable periodontal prognosis were excluded. Preparations had chamfer margins, incisal reduction, palatal overlap, and at least 80% enamel. Feldspathic veneers from refractory dies were etched (hydrofluoric acid), silanated, and bonded. Many patients received more than 1 veneer (mean: 5.8 ± 4.3). Clustered outcomes were accounted for by randomly selecting (random table) 1 veneer per patient for analysis. Clinical outcome (success, survival, unknown, dead, repair, failure) and Kaplan-Meier estimated cumulative survival were reported. Differences in survival were analyzed using the log-rank test. Results: For the random sample of veneers (n = 155), the estimated cumulative survival rates were 96% ± 2% (10 years) and 96% ± 2% (20 years). For the entire sample, the survival rates were 96% ± 1% (10 years) and 91% ± 2% (20 years). Survival did not statistically differ between these groups (P = .65). Seventeen veneers in 8 patients failed, 75 veneers in 30 patients were classified as unknown, and 407 veneers in 130 patients survived. Multiple veneers in the same mouth experienced the same outcome, clustering the results. Conclusions: Multiple dental prostheses in the same mouth are exposed to the same local and systemic factors, resulting in clustered outcomes. Clustered outcomes should be accounted for during analysis. When bonded to prepared enamel substrate, feldspathic porcelain veneers have excellent long-term survival with a low failure rate. The 21-year estimated cumulative survival for feldspathic porcelain veneers bonded to prepared enamel was 96% ± 2%.