Aims: We aimed to compare conventional rigid cast immobilization with the semi-rigid functional treatment method with respect to calf muscle atrophy, ankle range of motion (ROM) and patient satisfaction in patients who had acute lateral ligament injury of the ankle. Methods: Sixty patients were randomized into the functional immobilization group (Group SC) or conventional belowthe- knee walking cast (Group R). Muscle atrophy was evaluated by axial Computerized Tomography and ankle ROM were recorded before and after treatment. A brief questionnaire for the evaluation of patient satisfaction was applied after the casts were removed. Results: A reduction in muscle area indicating atrophy was detected for both groups (p< 0.001). However, the atrophy was more pronounced in Group R for anterior and superþcial posterior muscle groups. There was also a reduction in ankle ROM for both groups. The loss of ROM for Group R was more evident and differences between the groups were statistically signiþcant. The patients who were treated with functional immobilization techniques were more satisþed. Mean score for Group SC was 67±12 where as it was 28±7 for Group R (p< 0.001). Conclusions: Functional immobilization has shown better results on patient satisfaction and ankle ROM. Although not statistically signiþcant, functional group also showed better results with respect to muscle atrophy for all muscle groups except the lateral. Regarding the previous literature on the effectiveness of functional immobilisation on ankle stability, this technique additionally brings advantages to the treatment of ankle ligamentous lesions with regard to patient satisfaction and facilitation in rehabilitation.