OBJECTIVES: To investigate the impact of knee pain and low back pain (LBP) on quality of life (QoL) in people ≥50 years of age. DESIGN: Cross-sectional study. SETTING: A nationwide survey. PARTICIPANTS: A total of 1295 men and 1658 women aged ≥50 years from the Fifth Korea National Health and Nutrition Examination Survey, conducted in 2010. METHODS: Knee pain and LBP were assessed by a questionnaire, and QoL was assessed by the EuroQol (EQ)-5D, consisting of the EQ-5D descriptive system and the EuroQol visual analogue scale (EQ-VAS). Multiple linear regression models were used to evaluate associations between knee pain or LBP and the EQ-5D index or EQ-VAS score. MAIN OUTCOME MEASUREMENTS: Standardized coefficient (β) for QoL according to the presence of knee pain or LBP. RESULTS: Both men and women with knee pain or LBP had a lower QoL than those without them in all dimensions of the EQ-5D, EQ-5D index, and EQ-VAS scores. Compared with most other chronic diseases, knee pain and LBP showed stronger negative correlations with the EQ-5D index and EQ-VAS score. In men, LBP showed a stronger negative correlation with the EQ-VAS score than knee pain. The relative impact of LBP on knee pain was greater in people aged ≥65 years than in people aged 50-64 years, especially men. CONCLUSIONS: These results suggest that knee pain and LBP are important factors affecting QoL in middle-aged and elderly people and that LBP may be relatively more important than knee pain in elderly people, especially men. Proper management and prevention of these conditions can help to improve QoL.