Health education materials, medical instructions, consent forms, and self-report questionnaires are often given to patients with little regard for their ability to read them. Reading ability is rarely tested in medical settings. The Rapid Estimate of Adult Literacy in Medicine (REALM) was developed as a quick screening tool to assist physicians in identifying patients with limited reading skills and in estimating patient reading levels. This information can be used to tailor materials and instructions to patients' abilities. The REALM and the reading sections of the Peabody Individual Achievement Test-Revised and the Slosson Oral Reading Test were used to test reading ability in 207 adults in six public and private primary care clinics. REALM scores correlated highly with those of the standardized reading tests. The REALM, which takes three to five minutes to administer and score, appears to be a practical instrument to estimate patient literacy in primary care, patient education, and medical research.