BACKGROUND: The generation of the use of informed consent forms makes necessary to grant their legibility for patients. Up to now, we didn't have in Spain a suitable yardstick for evaluating the reading levels, METHODS: A Sample of 10 texts of diverse precedence, 8 journals and 16 informed consent forms were collected, They were analyzed using the Grammatik 6.0 utility of the word processor Word Perfect 6.1, and four parameters were obtained: number of words, number of sentences, Fesch-Kincaid Grade Level and Sentence Complexity. In addition an Integrated Readability Level (LEGIN) was calculated. RESULTS: Flesch Level and Sentence Complexity give a suitable and complementary analysis of readibility, wich is inhanced by the LEGIN, The acceptably reading level is obtained when the Flesch-Kincaid Level is above 10, the Sentence Complexity is under 40 and, overcoat, the LEGIN is above 70. Just 5 of the 16 consent forms had the adequate LEGIN level. Another 5 had the Flesch correct levels and 7 the adequate Sentence Complexity. CONCLUSIONS: The Grammatik utility of the word processor Word Perfect 6.1 is a suitable yardstick to analyze the readibility, but is necessary to complete the analysis with the LEGIN, to render more sensibility and especificity, It's mandatory to enhance the readability of written forms to grant the ethical quality of the informed consent process.