Medical discharge documents are summaries written by a physician about the patient’s condition and aim at transferring information to other health care personnel but also to the patient. According to the legislation, the patient should be able to understand the document. In practice, however, this has been shown to be problematic. This paper studies discharge documents from the patients’ perspective and examines how they fulfil the legislation’s demands on understandability. Concentrating on the vocabulary of the texts, we analyse the frequency of domainadapted terms, abbreviations and foreign words. The material consists of 23 528 heart patients’ discharge documents (5 747 126 words). The analysis is performed with the morphological analyser FinTWOL (http://www2.lingsoft.fi/cgi-bin/fintwol). Altogether, FinTWOL analyses 24% of the corpus as unknown or foreign words, abbreviations or medical terms. The most common category, unknown words, includes misspellings and medical terms, such as l.dex. Of these, 100 most common cover for 43% of the total. These terms thus seem to be relatively fixed. Of the words analysed as abbreviations, some are common also in standard language, but others are still very domain-specific, such as I.V. (intravenous). Also the used abbreviations are very fixed: the 100 most common ones cover for 94% of the total. This, however, does not help the patient who probably reads only one document. Similarly, even though misspellings are globally infrequent, they still occur more than once per document. In order to place the obtained results in a context, we performed a similar analysis on general Finnish university newspaper text from Turku Dependency Treebank. In comparison with the 24% obtained with the discharge documents, from the total of 10 687 words, 8,6% were given a special tag. The results show that that terms and abbreviations are considerably more used in discharge documents than in general newspaper text. It is clear that a text with such a vocabulary is domain-specific and distinct from the language that the patient is used to. Also e.g. the varying use of upper and lower case letters (dg and DG for diagnosis) emphasize the particularity of the language. In standard language texts such writing would not be acceptable. Standard writing would, however, help the patients to better understand the texts.