The Convention on the Rights of Persons with Disabilities recognizes full legal capacity in any person, regardless of disability, and this has caused, in general terms, a rethinking of the idea of autonomy of the will. This new reality modifies the way of conceptualizing and interpreting the declaration of will in the general theory of legal act, especially, when the natural capacity to know and want can come naturally limited by a psychic disability or by a coma state. The internal formation of the will and its manifestation are a complex matter, above all when the supports might not be enough to know the true will of the person suffering from any of those disabilities. For all these reasons, this paper analyzes the article 141 of Peruvian Civil Code, regulator of the declaration of will, in order to offer general guidelines that make it possible to know adequately, and rebuild, in some cases, the will of persons with disabilities, depending on each situation.