BACKGROUND: The purpose of this feasibility study was to begin to determine the efficacy of cylinder cast immobilisation compared to no form of immobilisation for patients following first-time patellar dislocation (FTPD). MATERIALS AND METHODS: Participants were patients who attended a National Health Service Accident and Emergency department following a FTPD. Patients were randomised to receive immobilisation for four weeks in a cylinder cast followed by rehabilitation, versus no immobilisation and early rehabilitation. All patients were followed-up over a three month period, assessed using the Visual analogue scale for pain, Short Form-36, the Lysholm knee score and the Modified Functional Index. RESULTS: Forty-one patients were approached to participate. Eight satisfied the pre-defined eligibility criteria and were randomised between the two groups. Whilst the results indicated a trend for superior short-term functional outcomes for those patients not immobilised compared to those immobilised following a FTPD, the small sample and baseline imbalances between the groups may have had a substantial influence on the results. CONCLUSION: This feasibility study has indicated that the outcome measurements adopted were appropriate to answer this research question, but the assessment of return to normal activity, recurrent instability and dislocation and cost-effectiveness over a longer follow-up period is recommended. Similarly, defining a more pragmatic eligibility criteria and recruiting from multiple centres would be recommended for the definitive trial requiring a sample of 348 patients to demonstrate a statistical significant treatment effect. LEVEL OF EVIDENCE: Level 2b.