Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly prescribed for the treatment of signs and symptoms of osteoarthritis (OA). Nabumetone and oxaprozin are 2 of the newer NSAIDs and have been shown to have similar safety and efficacy profiles. Nabumetone 1000 mg to 1500 mg once a day (QD) and oxaprozin 1200 mg QD are commonly recommended doses. This study compared the health-related quality of life (HRQOL) of patients receiving oxaprozin 1200 mg QD with that of patients receiving nabumetone 1000 mg QD or nabumetone 1500 mg QD for the treatment of signs and symptoms of OA of the knee. Two similarly designed, independent, randomized, double-masked, placebo-controlled clinical trials were conducted. In trial 1, patients were randomized to receive oxaprozin 1200 mg QD (n = 109), nabumetone 1000 mg QD (n = 110), or placebo (n = 109); in trial 2, patients received oxaprozin 1200 mg QD (n = 116), nabumetone 1500 mg QD (n = 115), or placebo (n = 116). HRQOL was measured by the Medical Outcomes Study Short-Form-36 Health Survey (1-week recall period) at baseline and weeks 2 and 6. Data from the 2 trials were combined to assess differences across the 4 groups in 8 domains and 2 summary scores at baseline, and changes in HRQOL scores at weeks 2 and 6. At week 2, the oxaprozin group showed significantly greater improvement than the placebo group in role physical, vitality, and mental component summary (MCS) scores (P < 0.05), and in physical functioning, bodily pain, social functioning, and physical component summary (PCS) scores (P < 0.01). The nabumetone 1500-mg group showed significantly greater improvement than the placebo group in bodily pain and social functioning (P < 0.05), and in vitality and MCS score (P < 0.01). No significant differences were observed between the nabumetone 1000-mg and placebo groups. At week 2, the oxaprozin group showed a greater change than the nabumetone 1000-mg group in PCS score (P < 0.05). At week 6, oxaprozin treatment resulted in significantly greater improvement than placebo in physical functioning, role physical, and bodily pain (P < 0.05); social functioning, role emotional, and mental health (P < 0.01); and vitality and MCS score (P < 0.001). The nabumetone 1500-mg group showed significantly greater responses than the placebo group in vitality (P < 0.05), mental health (P < 0.01), and MCS score (P < 0.001). The oxaprozin group had significantly better scores than the nabumetone 1500-mg group in the PCS (P < 0.05), and it showed significantly greater improvement than the nabumetone 1000 mg group in role physical and PCS score (P < 0.01) and in role emotional (P < 0.05). No statistically significant differences were found between placebo and nabumetone 1000 mg at week 6. Results of this study suggest that oxaprozin 1200 mg QD has a significant positive impact on the HRQOL of patients with OA of the knee compared with nabumetone 1000 mg QD and placebo.