Aims - A systematic review of the studies on use of alternative and complementary medicine by mental health services' users to investigate the prevalence and motivations of CAM used to treat mental disorders. Methods - This paper shows a part of the results of a literature review, limited to studies between 1966 and 2005, was carried out using Ovid Medline, PsycINFO and EBM Reviews databases. This was supplemented by hand searching of reference lists. Results - Ninety-one studies on CAM's use by psychiatric patients were analyzed. In this paper the twenty-five articles about the CAM's prevalence and use's motivations are described. The use of complementary and alternative medicine (CAM) varies across countries: data suggest that from 50% to 80% of people suffering of mental disorders use CAM. Heterogeneous methods, samples and results characterizing the studies make generalizations results difficult. Patients motivations of CAM's use were poorly investigated by research, however it seems that persons affected by mental disorders use MAC prevalently because they are dissatisfied with conventional medicine and/or because these alternatives approaches are congruent with their own values, beliefs and philosophical orientation toward health care. Conclusions - The review emphasize the importance of a best physicians' education and information about CAM to improve the management of non-conventional and orthodox medicine relationship. The motivations of CAM's use underline the relevance of patient's holistic conception and the therapeutic role of a patient-physician relationship based on emphaty. Besides it seems important to investigate furtherly patients' psychological and social aspects that influence their choise to use CAM.