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Taking relevant decisions (in our own interest or in that of our relatives) is necessary for our adaptation, our autonomy, and our survival. However, decision-making is a complex and composite ability, which is particularly sensitive to the effects of aging. Two decision-making conditions are usually distinguished: decision under ambiguity, in which the probability of the result is ignored, and decision under risk, in which the consequences and the probabilities of these consequences are known. This review outlines the major age-related changes in decision-making processes. In normal aging, impaired decision-making is mainly related to executive function decline, and decision under risk seems to be better preserved than decision under ambiguity. During pathological aging, the location of the cerebral lesions has a significant impact on the type of decision-making problems encountered. Thus, frontal and/or sub-cortical frontal lesions lead to greater risk-taking, especially in ambiguous conditions. In this condition, reinforcements have a prevalent role. Frontal and/or sub-cortical frontal lesions make these reinforcements particularly inefficient, hindering the ability to anticipate the probability of the outcome. Impaired decision-making under risk is related to executive dysfunctions and damage of the expected reward system. The patients become unable to recognize and anticipate the consequences and their probabilities on the outcome. Temporal or temporofrontal lesions affect decision-making under ambiguity and decision making under risk. Impairment of risky decisions is due to the inability to accurately estimate the probabilities of the consequences. Decision-making disorders under ambiguity are linked with difficulties with learning by “feedback” and anticipating the likelihood of the outcome. These results highlight the complexity and variety of mechanisms and processes of decision-making activities. These data also help to explain the dissociation observed, depending on the type of brain damage identified in the context of normal and pathological aging.