The law assumes that all adults have “legal capacity” until it is proven otherwise. in the elderly, mental incapacity is mostly observed in advanced dementia. However, normal aging frequently carries with it some degree of cognitive impairment, placing seniors more vulnerable to the influence of others, therefore being less able to make wise and sensible decisions. with regard to donations, this are only legally legitimate if at the time of the event the donor was able to understand the nature of the transaction, weigh its consequences and determine for himself to be in agreement with it. From the point of view of forensic psychiatry, the evaluation of these assumptions is a challenge, reflecting the difficulty in assessing, retrospectively, the subject's cognitive functions at the time of the event. in cases where the cross-sectional evaluation favours the diagnosis of dementia it's crucial to objectify the onset and course of the illness. To achieve this goal, the familial, medical, imagiological and psychometrical data must be considered and valued in accordance to current scientific medical knowledge. in Portugal, the literature is scarce regarding this issue. in this work the authors propose to discuss this matter, presenting a case report of a donation from father to sons, involving a great deal of money, made by an 85-year-old man, who had suffered an ischemic cerebrovascular accident 5 years before.