Background Involvement of mental health-care patients in the decision-making processes is considered to be an ethical requirement. Health-care systems worldwide are increasingly emphasizing the value of participatory approaches. There is, however, no consensus on the definition of patient involvement. The literature is particularly inconsistent and lacks clarity. Objective The purpose of this article is to clarify the concept of patient involvement in mental health care (MHC), taking into account its multidimensional nature. Search strategy We searched the literature in online databases from January 1998 until August 2010 using synonyms of 'patient involvement', combined with the terms 'mental health(care)'. Data synthesis Based on 45 different descriptions found in the literature, we constructed a definition of patient involvement and we drew up a model identifying its determinants and outcomes. Results We propose a comprehensive model of patient involvement to be used in MHC. This model can serve as a guide for policy makers and field workers to shape policies to stimulate involvement. Discussion and conclusions There are three main problems in the literature concerning patient involvement. First, there is a proliferation of conceptualizations of the topic, leading to conceptual vagueness. Furthermore, there is a lack of quantitative data, and some aspects of involvement remain underexposed, such as the involvement of specific target groups and practical ways to shape the involvement processes. Involvement processes should be tailored to the specific target group and context.