This study is a corpus-based lexical analysis of subject-specific university textbooks which purports to explore lexical text coverage and frequency distribution of words from the Academic Word List and the British National Corpus frequency-based word families. For this study a 508,802-word corpus was created, the findings of which reflect that the Academic Word List word families constitute only a small coverage (6.5%) of the words in the entire corpus, whereas the first two thousand high-frequency word families give the coverage of 88.92%. In terms of the text coverage, the results reveal that if 98% coverage of a text is needed for unassisted comprehension, then a vocabulary size of 9000 word families is required. The results also substantiate the claims that the Academic Word List is not as general an academic vocabulary as it was initially intended to be and, more importantly, supports the assumption that students need a more restricted core academic vocabulary. It is therefore argued that 127 academic word families which are relatively frequent in the overall university textbook corpus can be used as a part of the university word list for second-year English majors who have to read and comprehend university textbooks.