The written informed consent form (WICF) provides information that must be written in simple, easily understood language, highlighting voluntary participation safeguards, risks, possible benefits, and procedures. Currently, the possibility that research subjects do not fully understand the text of the WICF or their rights as participants, despite having signed the WICF and agreed to participate in the study, has been a point of discussion.To evaluate the readability of the WICFs, as well as to correlate research subject acceptance of the WICF with demographic status, social factors, risk-benefit relationship, and education level.The study involved 793 patients treated in public or private hospitals and asked to give informed consent for their inclusion. Were reviewed patient medical charts in order to obtain demographic and social data, and was used the Flesch Reading Ease and the Flesch-Kincaid Readability Indices to evaluate the reading level of the WICF texts.Acceptance was higher (99.7%) among patients treated in public health care facilities and among patients (99.73%) who participated in protocols involving lower risk. Although acceptance was not influenced by education level, 462 patients (58.26%) had eight or less years of schooling. The obtained readability index ranged from 9.9 to 12 on the Flesch-Kincaid test, and from 33.1 to 51.3 on the Flesch Reading Ease test.The WICFs had high degree of reading difficulty. Although patient acceptance was not found to be related to demographic or social factors, it was found to be influenced by the risk-benefit relationship.