For 16 years, the Hamilton Family Health Team Mental Health Program has successfully integrated mental health counselors, addiction specialists, child mental health professionals, and psychiatrists into 81 offices of 150 family physicians in Hamilton, Ontario. Maximising the potential of a "shared care" model requires changes within the primary care setting, to support the addition of mental health and addiction professionals, active involvement of primary care staff in managing mental health problems of patients, and collaborative practice. This coordinated effort allow mental health treatment through onsite support from a mental health team and supplants the need to refer most patients to the mental health setting. This article reviews the evolution of the program and the changes made by practices with key lessons learnt.