A prominent feature of formal writing, particularly in the field of science and technology, is the use of nominalization. Scientific writings, including medical writings, are expected to observe formality, precision, lack of ambiguity and concentration of highly technical terms. In such genres, the use of nominalization, affecting the lexical density of the text, plays a key role. In this connection, the purpose of this study was to compare the use of nominalization and the level of lexical density in medical academic articles written by native English writers and their Iranian counterparts based on the theory of grammatical metaphor proposed by Halliday (1985). To this end, the abstract section of 20 authentic English medical articles written by native English writers and 20 abstracts written by Iranian authors, drawn from highly influential medical journals, were selected. These abstracts were analyzed and compared based on the frequency of nominalization used and the level of lexical density in them. The findings revealed that Iranian writers used less nominalization in their writings.