The purpose of this study was to characterize students' self-assessments when reading mathematical texts, in particular regarding what students use as a basis for evaluations of their own reading comprehension. A total of 91 students read two mathematical texts, and for each text, they performed a self-assessment of their comprehension and completed a test of reading comprehension. Students' self-assessments were to a lesser degree based on their comprehension of the specific text read but based more on prior experiences. However, the study also produced different results for different types of texts and for different components (or levels) of reading comprehension.