Patient information leaflets are an important adjunct to verbal exchange between doctor and patient. Their value is dependent upon whether they contain useful information from the viewpoint of the patient and are easily understood. We developed a framework based upon linguistic theory for assessing the quality of written patient information and applied it to a set of leaflets about methotrexate treatment. Items included the overall structure of the text, the technicality of the vocabulary used, the number of content words per clause ("lexical density"), and the clarity of the role relationship between author and reader. The leaflets consisted of up to nine identifiable sections (range 3-8): background information about the drug, summary of its use, dosage instructions, outline of benefits and side-effects, monitoring information, constraints on patient behavior, storage instructions, and clinical contact availability. Most leaflets contained a high number of content words per clause and the identity of the author was clear in only three (17%). Linguistic analysis provides highly relevant information about written patient information. Together with critical assessment of factual and visual aspects, consideration of key linguistic features should improve the quality of informational texts for our patients. (Contains 3 tables and 1 figures.)