The general rules for elicitation of symptoms during the Mental State Examination (MSE) are not usually emphasized during the training of mental health professionals. This paper discusses principles which can be used to elicit and establish symptoms. The issues include the gold standard, demarcation of abnormalities, screening and confirmation, changes in population characteristics, prevalence and predictive values. The Bayesian framework is elaborated. The principles of elicitation should be emphasised during the training so that trainees have a more rational basis for the use of the MSE.