Patient education materials and hospital forms are given to patients with little regard for their ability to read them. Nationwide sampling and data from the 1980 census suggest that a high proportion of patients cared for in public hospitals are functionally illiterate. In this study, 151 adult primary care patients in five different ambulatory care settings were tested for reading comprehension. Patient education materials and forms from each clinic were analyzed for readability using a standard computer program. A large discrepancy was found between the average patient reading comprehension and the ability levels needed to read patient education materials. The average reading comprehension of public clinic patients was 6th grade 5th month. Most tested patient education materials required a reading level of 11th to 14th grade, and standard institutional consent forms required a college-level reading comprehension. In the public clinics there was a gap of more than 5 years between patient reading levels and the comprehension levels required by written patient materials.