Keloid scars are difficult to manage and remain a therapeutic challenge. Corticosteroid therapy alone or ionising radiation (radiotherapy) alone or combined with surgery are first-line treatments, but the scientific justification for these treatments is unclear. The aim of this systematic review and meta-analysis of randomised controlled trials (RCTs) is to assess the effects of intralesional corticosteroid injection in treating keloids or preventing their recurrence after surgical removal. Searches for RCTs were conducted through the MEDLINE, EMBASE, EBSCO and Cochrane databases from January 1974 to September 2017. Two authors independently reviewed study eligibility, extracted data, analysed the results, and assessed methodological quality. Sixteen RCTs that included more than 814 patients were scrutinised. The quality of evidence for most outcomes was moderate to high. In 10 RCTs, corticosteroid intralesional injections were compared with 5-fluorouracil, etanercept, cryosurgery, botulinum toxin, topical corticosteroid under a silicone dressing, and radiotherapy. Corticosteroid intralesional injections were more effective than radiotherapy (RR 3.3, 95% CI: 1.4–8.1) but equipotent with the other interventions. In conjunction with keloid excision, corticosteroid treatment was compared with radiotherapy, interferon α-2b and verapamil. In two RCTs, there were fewer keloid recurrences (RR 0.43, 95% CI: 0.21–0.89) demonstrated with adjuvant radiotherapy than with corticosteroid injections. More high-quality, large-scale RCTs are required to establish the effectiveness of corticosteroids and other therapies in keloid management.