There is debate about the correspondence between prevalence estimates of mental disorders from large epidemiologic surveys and the measurement of need for psychiatric services in the community. There is also a growing consensus that a significant proportion of cases remains untreated in the community. This dissertation addresses the problem of need and use of mental health services for depression, alcohol dependence, social phobia, panic disorder, and agoraphobia, from five perspectives. First, it provides an estimate of the need for mental health services in the community, independent of diagnosis, and compare it to estimates based on prevalence data. Second, it provides data demonstrating the contrast between those who use and those who do not use mental health services. Third, it assesses how insight affects the likelihood of using services for mental disorders. Fourth, it measures the sensitivity and specificity of the Global Assessment of Function (GAF) in identifying need for services. Fifth, it investigates two possible sources of bias in samples of treated individuals: the role of psychiatric comorbidity and that of family history of mental disorders in use of services.