Developing reading skills in a second language presents learners with many challenges, including lexico-grammatical decoding. An additional challenge is posed by the different registers of written text and the associated lexico-grammatical features with which learners must contend. Questioning the efficacy of using non-academic reading texts in university-based intensive English programs in the United States, the present study is a comparative analysis between the language in texts commonly used in reading skill development classes (e.g., biographies, newspaper or news magazine articles) and the language in texts more commonly encountered in introductory undergraduate university classes, represented by a corpus of lower-division university textbook excerpts. Features compared include Academic Word List (AWL) vocabulary (Coxhead, 2000), nominal modification features, and surface features associated with readability. Findings suggest significant differences in percentage of AWL vocabulary and use of nominal modification, but no significant difference in features traditionally associated with readability. The paper proposes that the sentence internal language in the ESL textbook texts is not representative of language in university textbooks, neither introductory university textbooks in general nor introductory university textbooks by macro discipline, and that further consideration must be given to text selection and inclusion of supplemental texts and activities to account for lexico-grammatical differences. (Contains 4 tables and 3 figures.)