We examined whether the text understanding of students holding naive and sophisticated epistemological beliefs was differentially affected by text format, also controlling for effects of gender, word decoding, and prior knowledge on understanding. The participants were 39 Norwegian first-year teacher students, and the topic of reading was attention-deficit hyperactivity disorder (ADHD). It was found that only readers holding sophisticated epistemological beliefs displayed adequate understanding when reading multiple, partly conflicting, texts about ADHD, whereas students holding naive epistemological beliefs gained better understanding when reading a single textbook-like source with identical content. This finding, however, depended on the level of understanding being measured by the criterial task, with only the task measuring deeper situational text understanding showing an interaction between epistemological beliefs and text format. This study provides evidence that not only knowledge itself, but also personal beliefs about knowledge, may enhance or constrain deeper understanding of multiple texts. (Contains 4 tables.)