This study examined whether the reading passages in the new series of English-language textbooks for high-school students in Vietnam fostered reading comprehension and incidental vocabulary acquisition through reading by looking at four factors: the number of unfamiliar words in the texts, the importance of these words for text comprehension, the usefulness of contextual clues for interpreting the meanings of these words, and the frequency of these words within and across the texts. Results showed that most of the reading passages were overloaded with novel words and few of these words were important for text comprehension. Rarely did these words reoccur in the texts and the chance for successful lexical inferencing was extremely slim due to the paucity of useful contextual clues. These findings provide useful implications for both second language (L2) instructors and textbook writers inside and outside of this context.