OBJECTIVES: to evaluate the role of childhood intelligence and white matter hyperintensities (WMH) in the prediction of the trajectory of fluid intelligence in healthy old people from age 78 to 81. DESIGN: observational follow-up study from 1999 to 2002. SETTING: a university teaching hospital in Aberdeen, UK. Participants: a total of 106 volunteers born in 1921, with childhood intelligence records at 11, recruited 1997-98 to a follow-up study. MEASUREMENTS: participants underwent brain MRI in 1999-2000, to obtain measurements of brain WMH using Scheltens’ scale and a test of fluid intelligence (Raven’s Progressive Matrices) on three occasions between 1999 and 2002. RESULTS: in a latent growth model, we found a significant association between childhood intelligence and the intercept, but not the slope, of fluid cognitive ability in late adulthood. Similarly, baseline WMH score was associated with the intercept of late life cognitive ability, but not the slope. Age at imaging was associated with slope but not intercept. There was no significant association between sex and intercept or slope of late life cognitive ability. CONCLUSIONS: results suggest that brain MRI measures of WMH (attributed to cerebrovascular disease) and childhood intelligence significantly contribute to late life fluid cognitive ability but not to the trajectory of age-related change in fluid intelligence. We also show that age is associated with the cognitive trajectory from 78 to 81 years, even within our narrow age range sample. This may be a consequence of the recruitment pattern, with those having greater WMH burden, and who subsequently declined, being recruited later in the study.