Objectives To determine the lifetime quality-adjusted life years (QALYs) gained by total joint arthroplasty (TJA), and assess the QALYs attributed to specific postoperative rehabilitation interventions. Design Secondary analysis of 2 multicenter, randomized controlled trials (RCTs) with 3-, 6-, 12-, and 24-month follow-up. Setting Two university hospitals, 2 municipal hospitals, and 1 rural hospital. Participants Patients (N=827) who underwent total hip arthroplasty (THA) or total knee arthroplasty (TKA). Interventions RCT A: 465 patients were randomly assigned to receive aquatic therapy (pool exercises aimed at training of proprioception, coordination, and strengthening) 6 versus 14 days after THA or TKA. RCT B: 362 patients were randomly assigned to either perform or not perform ergometer cycling beginning 2 weeks after THA or TKA. Main Outcome Measure QALYs, based on the Short Form-6 Dimensions utility, measured at baseline and 3, 6, 12, and 24 months' follow-up. Results After hip arthroplasty, the lifetime QALYs increased by 2.35 years in the nonergometer group, and by 2.30 years in the early aquatic therapy group. However, after knee arthroplasty, the lifetime QALYs increased by 1.81 years in the nonergometer group, and by 1.60 years in the early aquatic therapy group. By ergometer cycling,.55 additional QALYs could be gained after hip and.10 additional QALYs after knee arthroplasty, while the additional QALYs attributed to the timing of aquatic therapy were.12 years after hip and.01 years after knee arthroplasty. Conclusions This analysis provides a sound estimate for the determination of the lifetime QALYs gained by THA and TKA. In addition, this analysis demonstrates that specific postoperative rehabilitation can result in an additional mean QALY gain of.55 years, which represents one fourth of the effect of surgery. Even if this is interpreted as a small effect at an individual level, it is important when extrapolated to all patients undergoing TJA. At a national level, these improvements appear to have a similar magnitude of QALY gain when compared with published data regarding medications to lower blood pressure in all persons with arterial hypertension.