OBJECTIVES: To describe inadequate pain relief (IPR) and evaluate its impact on QOL in patients with knee osteoarthritis. METHODS: SORT, a 12-month prospective study across 6 EU countries (N=1,260), enrolled participants > 50 years old with knee OA who were prescribed pain medications. Clinical history and QOL (generic and disease-specific) were collected at baseline and months 1, 3, 6, 9 and 12.  Inadequate Pain Relief (IPR) was defined as a Brief Pain Inventory (BPI) pain score of "moderate or greater pain" (score >4).  Statistical analyses of baseline data were conducted. RESULTS: Evaluable baseline data are presented for 1217 participants: 67.6% women; mean age 68 (SD=9.4) years; mean duration of OA 5.9 years (SD=6.2) and 83.4% reported taking oral pain medications.  IPR comprised 54% of the cohort (656 of 1217).  IPR participants reported more disability (14.3% vs. 9.3%, p=0.013), greater number of co-morbidities (p<0.0001) and were taking more opioid-containing medications (27.1% vs. 16.3%, p<0.001) than those with pain relief.  IPR participants had worse WOMAC scores: stiffness (56.9 vs. 33.6, p<0.001), pain (53.2 vs. 28.4, p<0.001) and physical function (54.9 vs. 29.9, p<0.001).  IPR participants reported significant worse scores for pain severity (5.8 vs. 2.7, p<0.001) and pain interference (5.3 vs. 2.4, p<0.001) as measured by BPI.  General health status was lower for IPR participants with 51.2% vs. 29.0% (p<0.001) reporting fair/poor health.  IPR participants scored worse on all SF-12 domains with differences for the physical component summary (PCS) (35.1 vs. 41.4, p<0.001) and mental component summary (MCS) (45.7 vs. 52.0, p<0.001).  CONCLUSIONS: SORT found over half of participants reported inadequate pain relief (i.e., moderate to severe pain). IPR participants experienced more co-morbidities and significant QOL impairments as demonstrated by poorer health status, greater pain, physical limitations and stiffness than participants with pain relief. The presented SORT baseline data support the relationship between IPR and reduced QOL.