BACKGROUND CONTEXT Due to poor bone stock in the elderly, with concerns of screw pull-out, a non-instrumented fusion is commonly performed in Scandinavia when lumbar instability is present. Allograft bone is often used as graft extender with consequent low fusion rates. In an attempt to increase fusion rates, we conducted an RCT comparing ABM/P-15 versus allograft in non-instrumented lumbar fusion surgery. Despite obtaining an overall fusion rate of 59% in the ABM/P-15 group compared to 35% in the allograft graft group based on 1-year postoperative fine cut CT-scans, Patient Reported Outcomes (PROs) at 2 years post operatively were similar between the two groups. PURPOSE To compare 5-year PROs of patients with non-instrumented posterolateral fusion due to degenerative spondylolisthesis with either 15 amino acid residue (ABM/P-15) or allograft. STUDY DESIGN/SETTING Randomized clinical trial. PATIENT SAMPLE Patients 65 years or older with spinal stenosis and degenerative spondylolisthesis (DS) who previously underwent decompression and non-instrumented posterolateral fusion a minimum 5 years prior. OUTCOME MEASURES Oswestry Disability Index (ODI), Visual analog scales (VAS) for Back (BP) and Leg Pain (LP) and EuroQOL-5D (EQ5D). METHODS A total of 101 patients were enrolled in the study and randomized 1:1 to either ABM/P-15 (mixed 50/50, 5cc/level) or allograft bone (30g/level), both mixed with local bone graft. PROs were collected at baseline and at 12, 24 and 60 months postoperative. RESULTS The two groups were similar in terms of sex distribution, age and number of levels fused at baseline. There were 98 patients available for analysis after 1 year, 90 and 78 patients after 2 and 5 years. Patients in both groups reported clinically and statistically significant improvements in all PROs from baseline to postoperative on all outcome measures. At 5 years follow-up, no significant differences were reported on LP (ABM/P-15=25,8 vs 32,0, p=0,36) or EQ5D (ABM/P-15=0,81 vs 0,74, p=0,21) whereas ODI (ABM/P-15=18,6 vs 27,0, p= 0,04) and BP (ABM/P-15=22,5 vs 38,4, p=0,02) were statistically significant better in the ABM/P-15 group. CONCLUSIONS At the 5-year follow-up period, patients who had non-instrumented posterolateral fusion augmented with ABM/P-15 had better ODI and BP scores compared to the allograft only group, despite showing similar PROs at the 2-year follow-up period. FDA DEVICE/DRUG STATUS ABM/P-15 (Investigational/Not approved)