OBJECTIVE To determine the ability of patients to complete successfully basic reading and numeracy tasks required to function adequately in the health care setting. METHODS Cross-sectional survey. METHODS Two urban, public hospitals. METHODS A total of 2659 predominantly indigent and minority patients, 1892 English-speaking and 767 Spanish-speaking, presenting for acute care. METHODS Functional health literacy as measured by the Test of Functional Health Literacy in Adults (TOFHLA), an instrument that measures ability to read and understand medical instructions and health care information presented in prose passages and passages containing numerical information (eg, prescription bottle labels and appointment slips). RESULTS A high proportion of patients were unable to read and understand written basic medical instructions. Of 2659 patients, 1106 (41.6%) were unable to comprehend directions for taking medication on an empty stomach, 691 (26%) were unable to understand information regarding when a next appointment is scheduled, and 1582 (59.5%) could not understand a standard informed consent document. A total of 665 (35.1%) of 1892 English-speaking patients and 473 (61.7%) of 767 Spanish-speaking patients had inadequate or marginal functional health literacy. The prevalence of inadequate or marginal functional health literacy among the elderly (age > or = 60 years) was 81.3% (187/230) for English-speaking patients and 82.6% (57/69) for Spanish-speaking patients, and was significantly higher (P < .001) than in younger patients. CONCLUSIONS Many patients at our institutions cannot perform the basic reading tasks required to function in the health care environment. Inadequate health literacy may be an important barrier to patients' understanding of their diagnoses and treatments, and to receiving high-quality care.