Background: Revision THAs are expected to increase; however, few studies have characterized the prognosis of revision THAs in younger patients. Questions/purposes: We performed a case-control study to evaluate intermediate-term survivorship, complications, and hip and activity scores after revision THAs in patients 55 years and younger, compared these outcomes with the results of primary THAs in a matched patient population, and evaluated risk factors for failed revisions. Methods: Ninety-three patients (103 hips) had a minimum of 4 years after revision THA, died, or had rerevision surgery. They were matched with 98 patients (103 hips) with primary THAs. Survivorship, complications, and clinical outcomes were compared between the groups using t-tests. Risk factors for failure also were assessed with chisquare analysis. Results: At mean followup of 6.7 years, 71 revision THAs (69%) survived, compared with 102 (99%) primary THAs (odds ratio [OR], 45.9; 95% CI, 16.5-128.4; p < 0.001). Complications occurred in 29% of the revision group and 6% of the primary group (OR, 6.64; 95% CI, 4.14-10.67; p < 0.001). After revision THA, the average improvement in Harris hip score was 19.2 compared with 34.4 after primary THA (p < 0.001). The UCLA activity score improved by an average of 0.87 after revision compared with 2.36 after primary THA (p < 0.001). Conventional polyethylene was associated with failure after revision THA (OR, 2.98; 95% CI, 1.87-4.76; p = 0.004). Conclusions: At intermediate-term followup, young patients undergoing revision THAs had markedly higher failure and complication rates and more modest clinical improvements compared with patients in a matched cohort who had primary THAs. Level of Evidence: Level III, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence.