Background: Currently the diagnosis of shoulder instability, particularly in children, is difficult and can take time. These diagnostic delays can lead to poorer outcome and long-term complications. A Diagnostic Decision Support System (DDSS) has the potential to reduce time to diagnosis improve outcomes for patients. The aim of this study was to develop a concept map for a future DDSS in shoulder instability.Methods: A modified nominal focus group technique, involving three clinical vignettes was used to elicit information physiotherapists decision-making processes.Results: Twenty-five physiotherapists, (18F:7M) from four separate clinical sites participated. The themes identified related to ‘Variability in diagnostic processes and lack of standardised practice’ and ‘Knowledge and attitudes towards novel technologies for facilitating assessment and clinical decision making’. Conclusion: No common structured approach towards assessment and diagnosis was identified. Lack of knowledge, perceived usefulness, access and cost were identified as barriers to adoption of new technology. Based on the information elicited a conceptual design of a future DDSS has been proposed. Work to develop a systematic approach to assessment, classification and diagnosis is now proposed.Trial Registration: This was not a clinical trial and so no clinical trial registry is needed.