Acute lateral ankle ligament ruptures are common problems in present health care. Early mobilisation and functional treatment are advocated as a preferable treatment strategy. However, functional treatment comprises a broad spectrum of treatment strategies and as of yet no optimal strategy has been identified. The objective of this review is to assess different functional treatment strategies for acute lateral ankle ligament ruptures in adults. We searched the Cochrane Bone, Joint and Muscle Trauma Group specialised register (December 2001), the Cochrane Controlled Trials Register (The Cochrane Library, Issue 4, 2001), MEDLINE (1966 to May 2000), EMBASE (1980 to May 2000), CURRENT CONTENTS (1993 to 1999), BIOSIS (to 1999), reference lists of articles, and contacted organisations and researchers in the field. Randomised clinical trials describing skeletally mature individuals with an acute lateral ankle ligament rupture and comparing different functional treatment strategies were evaluated for inclusion. Two reviewers independently assessed the quality of included 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 (WMD) for continuous outcome measures with 95 per cent confidence intervals (95%CI). Heterogeneity between trials was tested using a standard chi-squared test. Nine trials involving 892 participants were included. Lace-up ankle support had significantly better results for persistent swelling at short-term follow up when compared with semi-rigid ankle support (RR 4.19, 95% CI 1.26 to 13.98); elastic bandage (RR 5.48; 95% CI 1.69 to 17.76); and to tape (RR 4.07, 95% CI 1.21 to 13.68). Use of a semi-rigid ankle support resulted in a significantly shorter time to return to work when compared with an elastic bandage (WMD (days) 4.24; 95% CI 2.42 to 6.06); one trial found the use of a semi-rigid ankle support saw a significantly quicker return to sport compared with elastic bandage (RR 9.60; 95% CI 6.34 to 12.86) and another trial found fewer patients reported instability at short-term follow-up when treated with a semi-rigid support than with an elastic bandage (RR 8.00; 95% CI 1.03 to 62.07). Tape treatment resulted in significantly more complications, the majority being skin irritations, when compared with treatment with an elastic bandage (RR 0.11; 95% CI 0.01 to 0.86). No other results showed statistically significant differences. The use of an elastic bandage has fewer complications than taping but appears to be associated with a slower return to work and sport, and more reported instability than a semi-rigid ankle support. Lace-up ankle support appears to be effective in reducing swelling in the short-term compared with semi-rigid ankle support, elastic bandage and tape. However, definitive conclusions are hampered by the variety of treatments used, and the inconsistency of reported follow-up times. The most effective treatment, both clinically and in costs, is unclear from currently available randomised trials.