OBJECTIVE This study was performed to assess the impact of autologous conditioned serum (ACS) when added to preceding intra-articular glucocorticoid therapy on pain, function, and quality of life outcomes over 24 weeks. METHODS In this single-center, randomized controlled trial involving 40 patients with advanced knee osteoarthritis (Kellgren-Lawrence grades III and IV), ACS or saline placebo was injected after 40 mg triamcinolone acetonide (TA) intra-articular injection. Numerical rating scale (NRS) pain scores and Knee Injury and Osteoarthritis Outcome Score (KOOS) assessments were conducted at baseline and at weeks 3, 6, 12, and 24. The primary endpoint was the change in KOOS Pain at 24 weeks. Patient safety events were also monitored. RESULTS At week 24, TA + ACS significantly improved KOOS Pain, Symptoms, Activities of Daily Living, Quality of Life, and KOOS Sport scores. TA + ACS also outperformed TA + placebo in NRS pain scores (average and maximum intensity) at week 24 and NRS pain score (at rest) at weeks 12 and 24. The TA injection followed by ACS or placebo was well-tolerated. CONCLUSIONS ACS adds long-term pain relief and functional improvement to the short-term pain relief provided by glucocorticoids.