Our aim with this systematic review was to assess the effectiveness of various functional treatments for acute ruptures of the lateral ankle ligament in adults. We performed an electronic database search using MEDLINE, EMBASE, COCHRANE CONTROLLED TRIAL REGISTER and CURRENT CONTENTS. We evaluated randomized clinical trials describing skeletally mature subjects with an acute rupture of the lateral ankle ligament and compared functional treatments for inclusion in this study. 9 trials met our inclusion criteria. Two reviewers independently assessed the quality of these trials and extracted relevant data on treatment outcome. Where appropriate, results of comparable studies were pooled. Individual and pooled statistics are reported as relative risks (RR) for dichotomous outcome and (weighted) mean differences (W)MD) for continuous outcome measures with 95% confidence intervals (95% CI). Heterogeneity between the trials was tested using a standard chi-square test. Persistent swelling at short-term follow-up was less with lace-up ankle support than with semi-rigid ankle support (RR 4.2 95% CI 1.3-14), an elastic bandage (RR 5.5; 95% CI 1.7-18) and tape (RR 4.1; 95% CI 1.2-14). A semi-rigid ankle support required a shorter period for return to work than an elastic bandage (WMD 4.2; 95% CI 2.4-6.1) (p = 0.7). One trial reported better results for subjective instability using the semi-rigid ankle support than the elastic bandage (RR 8.0; 95% CI 1.0-62). Treatment with tape resulted in more complications, mostly skin problems, than that with an elastic bandage (RR 0.1; 95% CI 0.0-0.8). We found no other statistically significant differences. We conclude that an elastic bandage is a less effective functional treatment. Lace-up supports seem better, but the data are insufficient as a basis for definite conclusions.