Over the last two decades the Bech-Rafaelsen Mania Scale (MAS) has been used extensively in trials that have assessed the efficacy of treatments for bipolar disorder. The extent of its use makes it possible to evaluate the psychometric properties of the scale according to the principles of internal validity, reliability, and external validity.Studies of the internal validity of the MAS have demonstrated that the simple sum of the 11 items of the scale is a sufficient statistic for the assessment of the severity of manic states. Both factor analysis and latent structure analysis (the Rasch analysis) have been used to demonstrate this. The total score of the MAS has been standardised such that scores below 15 indicate hypomania, scores around 20 indicate moderate mania, and scores around 28 indicate severe mania.The inter-observer reliability has been found to be high in a number of studies conducted in various countries.The MAS has shown an acceptable external validity, in terms of both sensitivity and responsiveness. Thus, the MAS was found to be superior to the Clinical Global Impression scale with regard to responsiveness, and sensitivity has been found to be adequate, with the MAS able to demonstrate large drug-placebo differences.Based on pretreatment scores, trials of antimanic therapies can be classified into: (i) ultrashort (1 week) therapy of severe mania; (ii) short-term therapy (3 to 8 weeks) of moderate mania; (iii) short-term therapy of hypomanic or mixed bipolar states; and (iv) long-term (12 months) therapy of bipolar states. The responsiveness of MAS is such that the scale has been able to demonstrated that typical antipsychotics are effective as an ultrashort therapy of severe mania; that lithium and anticonvulsants are effective in the short-term therapy of moderate mania; and that atypical antipsychotics, electroconvulsive therapy (ECT) and transcranial magnetic stimulation seem to have promising effects in the short-term therapy of moderate mania. In contrast, the scale has been used to demonstrate that calcium antagonists (e.g. verapamil) are ineffective in the treatment of mania. MAS has also been used to add to the literature on the evidence-based effect of lithium as a short-term therapy for hypomania or mixed bipolar states and as a long-term therapy of bipolar states.