OBJECTIVES: In this study, a decision model analysis was performed, comparing the overall clinical efficacy and total costs in the treatment of tibial nonunions in the UK and in Germany. In the UK treatment with osteogenic protein 1 (OP-1) was compared to autograft or the Ilizarov fixation technique, and in Germany treatment with OP-1 was compared to fixation with a nail or a plate and if appropriate autograft. METHODS: The analysis was based on a decision tree. Data on efficacy were obtained from clinical trials and literature. Medical resource use data were obtained from country-specific expert panels. UK and German hospital direct medical costs of treatment were determined using standard costing techniques. The primary end-point was the total average cost of treatment of tibial nonunions. Univariate sensitivity analyses were performed to test the robustness of the model. RESULTS: In the UK, total cost per average patient receiving OP-1 treatment were £8797 compared to £9084 for autograft and £9722 for the Ilizarov fixation technique. The cost effectiveness ratio, cost per patient with a healed fracture, was comparable between the 3 treatment options; £10,860 for OP-1 treatment, £10,687 for autograft treatment and £10,234 for the Ilizarov fixation technique. In Germany, total cost per average patient receiving OP-1 treatment were €15,156 compared to €14,348 for usual care. The cost effectiveness ratio, cost per patient with a healed fracture, was better for usual care than for OP-1, but only slightly so. CONCLUSIONS: This study indicates that OP-1 is a good alternative treatment for tibial nonunions, both from a clinical and an economic perspective. Parameters influencing cost-effectiveness included % of adverse events and number of days in hospital. Prospective data is needed to confirm these results.