In a prospective randomized trial the early functional results after immobilisation in a cast were compared to those after using a vacuum stabilizing system. The vacuum stabilizing system Vacoped offers equivalent stability compared to a plaster cast. In contrast to the cast the Vacoped can be removed for body care and physical therapy. Additionally the range of motion for dorsal flexion/extention in the upper ankle joint can be adjusted. From 9/1996 to 7/1997 there were 40 patients included in the study with an operated ankle fracture as monotrauma. Six weeks postoperatively the patients with cast treatment showed significantly higher functional deficits for the upper ankle joint (20%), the lower ankle joint (40%) and muscle atrophy (2.1 cm side difference) than the group with the vacuum stabilizing system (upper ankle joint 15%, lower ankle joint 25%, 1.4 cm muscle atrophy). Five patients out of the group with the vacuum system were already at work three weeks postoperatively. Three months postoperatively the functional results for both groups were approximating. The vacuum stabilizing system Vacoped offers better early functional results than conventional cast treatment after osteosynthesis of ankle fractures. Because of the increased patient comfort and the early ability for physical therapy the vacuum stabilizing system is preferable to cast treatment.