As part of a larger project to examine the complexities of patient adherence to medical directions, the current study compares written information given with prescribed medicines to patients in the United States (US) and Spain suffering from two chronic diseases. First, the legal context of the voluntary nature of the provision of such information in the US, and the mandatory nature of provision in Spain, was explored. Then, 30 drugs in common use in both countries, 19 for cardiovascular disease and 11 for endocrine disorders, were identified and the texts of the corresponding patient-directed written information were included in an electronic corpus and analysed. Ten rhetorical features common to both the US and Spanish texts were identified. Differences were found in the placement of two of the features in relation to the complete text: information on ‘side effects’ and concerning ‘the need to seek medical advice’ appeared more frequently throughout the US texts than in the Spanish texts. Detailed lexical analysis showed more technical vocabulary in use in the Spanish texts.