Western societies currently face the aging of their populations. New challenges are experienced by health professionals who are involved in competency assessment that may necessitate a public guardianship. This assessment is complex and its consequences are significant. The Competency Assessment Tool (CAT) can be used to provide a rigorous, objective and ethical evaluation by an interdisciplinary team. The purpose of this study was to validate the CAT. To do this, a Delphi study was conducted among 33 experts from five professions (social worker, occupational therapist, physician, neuropsychologist and nurse), working in seven administrative regions of Quebec. An expert consensus on the content of the CAT was obtained in the first round of consultation. Thus, this study has validated an assessment and decision-making process (CAT) designed for health and social professionals. This decision model can guide the competency assessment of the ability of persons with cognitive impairment to take care of themselves and to manage their finances. Further studies will be necessary to support use of the CAT in practice