Patients with lateral epicondylitis (tennis elbow) are frequently treated with corticosteroid injections, in order to relieve pain and diminish disability. The objective of this review was to evaluate the effectiveness of corticosteroid injections for lateral epicondylitis. Randomised controlled trials (RCTs) were identified by a highly sensitive search strategy in six databases in combination with reference tracking. Two independent reviewers selected and assessed the methodological quality of RCTs that included patients with lateral epicondylitis treated with corticosteroid injection(s), and reported at least one clinically relevant outcome measure. Standardised mean differences were computed for continuous data and relative risks (RR) for dichotomous data. A best-evidence synthesis was conducted, weighting the studies with respect to their internal validity, statistical significance, clinical relevance, and statistical power. Thirteen studies consisting of 15 comparisons were included in the review, evaluating the effects of corticosteroid injections compared to placebo injection (n=2), injection with local anaesthetic (n=5), another conservative treatment (n=5), or another corticosteroid injection (n=3). Almost all studies had poor internal validity scores. For short-term outcomes (<or=6 weeks), statistically significant and clinically relevant differences were found on pain, global improvement and grip strength for corticosteroid injection compared to placebo, local anaesthetic and conservative treatments. For intermediate (6 weeks-6 months) and long-term outcomes (>or=6 months), no statistically significant or clinically relevant results in favour of corticosteroid injections were found. Although the available evidence shows superior short-term effects of corticosteroid injections for lateral epicondylitis, it is not possible to draw firm conclusions on the effectiveness of injections, due to the lack of high quality studies. No beneficial effects were found for intermediate or long-term follow-up. More, better designed, conducted and reported RCTs with intermediate and long-term follow-up are needed.