Background: The outcome of a removable (MOK-cast) versus a non-removable polyester wrap for acute lateral ankle ligament injury is unknown. Methods: Patients with grade II–III lateral ankle ligament injuries were randomized between treatment with a MOK-cast and a wrap. Primary outcome is the Karlsson score for function. Secondary outcomes are patient satisfaction and pain at 4 months follow-up. Results: Randomisation resulted in 53 and 54 patients per arm. Four month follow up was completed by 92% (n = 100). The mean Karlsson score improved from 20 to 87 (p < 0.01) in the wrap group and 20 to 90 (p < 0.01) in the MOK-cast group. In the MOK-cast group treatment satisfaction was higher (8.2 vs 7.8 p 0.04). Reported pain was higher in the first thirty days after injury (p < 0.01). Conclusions: Both wrap and MOK-cast are effective functional treatment options in acute lateral ankle ligament injury. MOK-cast is associated with increased patient satisfaction but higher VAS pain scores. Level of evidence: I.