Identification of mentally ill military conscripts is crucial, since these individuals may experience an exacerbation of their illness during training with dire consequences for them and the organization. This article describes the design of a study to validate a screening instrument for psychiatric disorders as well as to establish their prevalence among male army conscripts in Singapore. It involved a two-stage process: the conscripts were screened with a new instrument which we termed the Mental Wellness Screening Questionnaire; those who screened positive, and a random sample of those who did not, were administered the computerized Composite International Diagnostic Interview which was the gold standard in making the diagnosis. This study is unusual in that it involved almost the entire male population in 1 year but its relevance is the development of a screening instrument that can be used with ease in a large population of conscripts.