Adequate functional literacy skills positively influence individuals' ability to take control of their health. Print and Web-based cancer information is often written at difficult reading levels. This systematic review evaluates readability instruments (FRE, F-K, Fog, SMOG, Fry) used to assess print and Web-based cancer information and word recognition and comprehension tests (Cloze, REALM, TOFHLA, WRAT) that measure people's health literacy. Articles on readability and comprehension instruments explicitly used for cancer information were assembled by searching MEDLINE and PsycINFO from 1993 to 2003. In all, 23 studies were included; 16 on readability, 6 on comprehension, and I on readability and comprehension. Of the readability investigations, 14 focused on print materials, and 2 assessed Internet information. Comprehension and word recognition measures were not applied to Web-based information. None of the formulas were designed to determine the effects of visuals or design factors that could influence readability and comprehension of cancer education information.