Free and informed consent is an ethical and legal request in research involving human beings, seeking the manifestation of autonomy of the subject. However, autonomy is at risk when those involved are socio culturally vulnerable. In forensic cases, Law 12,654 of 2012 excludes the consent and makes mandatory the donation of biological materials by those convicted for heinous crimes. The aim of the study is to assess the level of damage to subjects referred for DNA testing at the Instituto de Pesquisa e Perícias em Genética Forense (IPPGF). We assessed the readability and normative appropriateness of the Informed Consent form (ICF) used. The study also tries to identify the degree of literacy and reading habits of donors relating to the correct understanding of the process. It was found that the ICF has degree of readability above that of the convicted sent to IPPGF and also had normative needs. Finally, it was found that many donors have restricted reading habits and literacy. The results led to profound changes in the procedure for obtaining consent for DNA forensic trials in IPPGF.