The informed consent form (ICF) is a critical document for ensuring patients are properly informed about participation in clinical trials, yet there are no regulations that govern the length and format of the document, for the texts reach an average length of 18 pages. The aim of the present study is to conduct a readability assessment, comparing a standard version ICF of 18 pages and a modified (shortened to 11 pages and illustrated) version ICF, using the methodology for the approval of patient information leaflets for marketed medications mandated in Poland and assessing two age groups--adults aged 18-65 and elderly >65. Ten adult and 10 elderly participants were included in the study. The long and short versions of the ICF resulted in different reading speeds in the adult group; the long version was read 75% faster than the short one on a words-per-minute basis, suggesting a less-thorough reading of the longer text. The difference in information retention, measured by a follow-up questionnaire, was over 20% better recall of risks, procedures, and benefits by the adult group readers of the short ICF. In the elderly group of participants, the retention and understanding of the documents was significantly lower overall (50% fewer correct answers in comparison to the adult group). In contrast to the adult group, the words-per-minute reading speed for the shorter version was 50% greater than for the longer. The elderly readers appeared to have reviewed the longer document more thoroughly while skipping the tabularized elements of the shortened document that were intended to simplify key information. A detailed analysis shows that the documents with visual aids were less effective for the elderly than plain text. Based on the information retention observed in this study, significant improvements in readability and design are needed for informed consent forms to fulfill their intended purpose. [ABSTRACT FROM AUTHOR]