The clinical, genetic or biological variables which regulate long-term efficacy of cholinesterase inhibitors (ChEIs) in Alzheimer disease (AD) are still unknown and it is not possible to predict who will benefit from the treatment. In this study we showed that high cholesterol levels correlated with faster decline at 1-year follow-up in AD patients on ChEIs. These findings suggest that serum cholesterol is a modulating factor of treatment response and additional therapies aimed at reducing treatable high cholesterol levels may represent an alternative strategy to improve ChEIs efficacy and slow down disease progression over time.