This paper presents the development of a mental health and addictions settings-specific Client Care Needs Assessment (CCNA) tool. The process of tool development was completed using a modified Delphi approach. During Round One, indicators reflecting the unique needs of patients with mental illness and addictions issues were identified through meetings with interprofessional teams. During Round Two, an interprofessional mental health practice expert panel further refined the tool via online survey. Round Three consisted of refining and finalizing the tool. The final CCNA tool consists of 31 indicators and 11 questions that are associated with the eight domains of the Synergy Model.