Simple English Wikipedia is a user-contributed online encyclopedia intended for young readers and readers whose first language is not English. We compiled a corpus of the entirety of Simple English Wikipedia as of June 20th, 2017. We used lexical frequency profiling tools to investigate the vocabulary size needed to comprehend Simple English Wikipedia texts. We hypothesized that if the texts are indeed simple, learners should need to know far fewer than 8000 words. Our findings indicate that the texts are not as simple as the creators of the authoring guidelines intended. We suggest that authors of simplified texts be encouraged to provide plain language explanations of low-frequency technical terms either in-text or in glossary form. We will discuss implications for researching the pedagogical usefulness of the Simple English Wikipedia. [For the complete volume, see ED578177.]