This study is the first in-depth qualitative study of service user involvement in the development of multidisciplinary mental health guidelines in the Netherlands. The study comprised a desk study of guidelines (n = 12) and case studies of service user involvement in five guidelines using document analysis, interviews (n = 24) and observations. The desk study shows that all multidisciplinary mental health guidelines have taken service user perspectives into account to some extent. The five guideline case studies led to the identification of ten main themes. Findings will assist guideline developers in making early, informed decisions on involving service users effectively.