To evaluate the cost-effectiveness IDET relative to circumferential lumbar fusion with femoral ring allograft (FRA). Cost-effectiveness analysis Patient-level data were available for patients with discogenic low back pain treated with FRA (n=37) in a randomized trial of FRA vs. titanium cage, and for patients recruited to a separate study evaluating the use of IDET (n=85). Patients were followed-up for 24 months. Oswestry Disability Index, visual analogue scale, quality of life (SF-36), radiographic evaluations, and NHS resource use. Cost-effectiveness was measured by the incremental cost per quality-adjusted life year (QALY) gained. Both treatments produced statistically significant improvements in pain, disability and quality of life at the 24-month follow-up. Costs were significantly lower with IDET due to a shorter mean procedure time (377.4 minutes vs. 49.9 minutes) and length of stay (7 days vs. 1.2 days). The mean incremental cost of IDET was -£3,713 per patient; the mean incremental QALY gain was 0.03. At a threshold of £20,000 per QALY the probability that IDET is cost-effective is 1, and the net health benefit is 0.21 QALY per patient treated. Both treatments led to significant improvements in patient outcomes which were sustained for at least 24 months. Costs were lower with IDET, and for appropriate patients IDET is an effective and cost-effective treatment alternative. Ethics approval: Ethics committee COREC This cost-effectiveness analysis was carried out by the York Health Economics Consortium at the University of York, and was funded by Smith & Nephew. Smith & Nephew had no financial or other involvement in the collection or analysis of the data on which the CEA is based.