Informed consent represents a specific protocol for obtaining consent from a fully informed human subject to take part in clinical research. Still, informed consent is not only required for clinical trials but it also represents a critical precondition before enrolment in standard everyday medical procedures. Relevant fundamental criteria for obtaining informed consent must be followed, and that is that patient must have the decisional capacity to reach autonomous decision. The patient must be adequately informed and not coerced. Evaluating decisional capacity (...) is crucial to providing the required level of care. The decision of which decisional capacity tool to use can be challenging because of various dissimilarities among the instruments. In this paper, four widely documented instruments have been evaluated, namely, the MacArthur Competence Assessment Tool for Treatment (MacCAT-T), the Hopkins Competency Assessment Test (HCAT), the Structured Interview for Competency/Incompetency Assessment Testing, Ranking Inventory (SICIATRI), and the Capacity Assessment Tool (CAT). Some of them include a fully structured interview; semi-structured forms characterise others. Most of them are adaptable for different scenarios, and yet, some are tailored for specific treatment decisions. Some evaluate all four components of decisional capacity, while others do not. Although a broad range of capacity assessment tools is available, it has been shown that they notably improve the accuracy of capacity evaluations. Given that many pathological conditions could result in impaired decisional capacity, physicians must be able to correctly and consistently assess the capacity for which education and previous experience are pivotal. (shrink)