Purpose: Functional treatment is the optimal non-surgical treatment for acute lateral ankle ligament injury (ALALI) in favour of immobilization treatment. There is no single most effective functional treatment (tape, semi-rigid brace or lace-up brace) based on currently available randomized trials. Methods: This study is designed as a randomized controlled trial to evaluate the difference in functional outcome after treatment with tape versus semi-rigid versus lace-up ankle support (brace) for grades II and III ALALIs. The Karlsson score and the FAOS were evaluated at 6-month follow-up. Results: One hundred and ninety-three patients (52 % males) were randomized, 66 patients were treated with tape, 58 patients with a semi-rigid brace and 62 patients with a lace-up brace. There were no significant differences in any baseline characteristics between the three groups. Mean age of the patients was 37.3 years (35.1–39.5; SD 15.3). Ninety-five males (49 %) were included. One hundred and sixty-one (59 + 50 + 52) patients completed the study through final follow-up; 32 % lost at follow-up. In two patients treated with tape support, the treatment was changed to a semi-rigid brace because of dermatomal blisters. Except for the difference in Foot and Ankle Outcome Score sport between the lace-up and the semi-rigid brace, there are no differences in any of the outcomes after 6-month follow-up. Conclusion: The most important finding of current study was that there is no difference in outcome 6 months after treatment with tape, semi-rigid brace and a lace-up brace. Level of evidence: I.