To assess the effectiveness of occlusal adjustment (OA) for treating temporomandibular disorders (TMD) in adults and preventing TMD. The Cochrane Controlled Trials Register, MEDLINE and EMBASE were comprehensively searched using the Cochrane methods. Reports and review articles were retrieved. Unpublished reports or abstracts were considered from the SIGLE database. All randomized or quasi-randomized controlled trials comparing OA with placebo, reassurance or no treatment in adults with TMD. The outcomes were global measures of symptoms, pain, headache and limitation of movement. Data collection and analysis followed the Cochrane Oral Health Group's statistical guidelines. Results showed no difference between OA and control group in symptom-based outcomes for treatment or incidence of symptoms for prevention. There is no evidence that OA treats or prevents TMD. OA cannot be recommended for the management or prevention of TMD. Future trials should use standardized diagnostic criteria and outcome measures when evaluating TMD.