Failure of the deinstitutionalization process and a tendency of limitating health care costs on the basis of evidence based medicine initiated planning mental health services according to the clients' needs. Defining needs is difficult due to the complexity of the concept of needs, so numerous definitions of needs have been proposed. In the health care context a need is most often regarded as the lack of health/wellbeing or the lack of access to care. Many clinical and population-based studies on needs were conducted in England and other well-developed countries. According to their results the most important are unmet needs, which correlate with unemployment, single status, low quality of life, low satisfaction with services and high social disability scores. Assessment of needs becomes a part of routine clinical practice and evaluation of mental health services. Results of such an assessment enables to fit the therapy and rehabilitation to the individual patient's needs which in consequence leads to a better therapeutic response and lower social disability. First Polish studies on needs of persons with different mental disorders indicate the social needs (company, intimate relationship and sexual expression) as the most often unmet from patient's point of view.