The progressive ageing of a population leads to an increase in the number of people suffering from cognitive deterioration. This requires particular attention in terms of the necessity to assess these people's cognitive functions and their capacity to make decisions. The present systematic review analyses the clinical and ethical aspects of any assessment of capacity, with a specific focus on the capacity of the individual to give informed consent for medical treatment and also with regard to their testamentary capacity. The results indicate that the concepts of capacity, competence and decision-making need to be better clarified, ad-hoc devised tools are required and a multidisciplinary, clinical and legal approach to assessments of capacity needs to be adopted. This is crucial to guarantee that the two ethical principles of capacity assessment are adhered to: respect for an individual's autonomy and the protection of fragile individuals
