This longitudinal study assessed cognition in Williams syndrome (WS) over a 5 year period using the same test battery over the two occasions of testing. The aim was to explore whether absolute levels of ability and relative cognitive strengths and weaknesses remain consistent over time. 27 participants with WS were assessed using the Woodcock Johnson Test of Cognitive Ability-Revised (WJ-R COG, Woodcock Johnson, 1989, 1990). Results suggested some developmental progress over time, but at a slower rate than typically developing peers. Cognitive strengths and weaknesses were consistent, at least on those abilities assessed using the WJ-R COG.