Observational studies have given conflicting results about the effect of statins in preventing dementia and cognitive decline. Moreover, observational studies are subject to prescription bias, making it hard to draw definite conclusions from them. Randomized controlled trials are therefore the preferred study design to investigate the association between statins and cognition. Here we present detailed cognitive outcomes from the randomized placebo-controlled PROspective Study of Pravastatin in the Elderly at Risk (PROSPER). Cognitive function was assessed repeatedly in all 5,804 PROSPER participants at six different time points during the study using four neuropsychological performance tests. After a mean follow-up period of 42 months, no difference in cognitive decline at any of the cognitive domains was found in subjects treated with pravastatin compared to placebo (all p > 0.05). Pravastatin treatment in old age did not affect cognitive decline during a 3 year follow-up period. Employing statin therapy in the elderly in an attempt to prevent cognitive decline therefore seems to be futile.