Three hundred and four participants in the Lothian Birth Cohort 1936 study took a validated IQ-type test at age 11 years and a battery of cognitive tests at age 70 years. Three tests of health literacy were completed at age 72 years; the Rapid Estimate of Adult Literacy in Medicine (REALM), the Test of Functional Health Literacy in Adults (S-TOFHLA), and the Newest Vital Sign (NVS). Participants who had a lower childhood IQ exhibited poorer performance on all three tests of health literacy taken in older adulthood. Relative cognitive change from age 11 to 70 and education were also important factors influencing performance on health literacy tasks, independent of childhood cognitive ability. It is important to understand the determinants of low health literacy in order to support individuals in managing their own health. (Contains 3 tables.)