Background: Autonomic function has received little attention in Alzheimer's disease (AD).ADpathology has an impact on brain regions which are important for central autonomic control, but it is unclear if AD is associated with disturbance of autonomic function. Objective: To investigate autonomic function using standardized techniques in patients with AD and healthy age-matched controls. Method: Thirty-three patients with mild to moderate AD and 30 age- and gender-matched healthy controls, without symptoms of autonomic dysfunction, underwent standardized autonomic testing with deep breathing, Valsalva maneuver, head-up tilt, and isometric handgrip test. Brachial pressure curve and electrocardiogram were recorded for off-line analysis of blood pressure and beat-to-beat heart rate (HR). Results: AD patients had impaired blood pressure responses to Vasalva maneuver (p < 0.0001) and HR response to isometric contraction (p = 0.0001). A modified composite autonomic scoring scale showed greater degree of autonomic impairment in patients compared to controls (patient: 2.1±1.6; controls: 0.9±1.1, p = 0.001). HR response to deep breathing and Valsalva ratio were similar in the two groups. Conclusion: We identified autonomic impairment ranging from mild to severe in patients with mild to moderate AD, who did not report autonomic symptoms. Autonomic impairment was mainly related to impairment of sympathetic function and evident by impaired blood pressure response to the Vasalva maneuver.Tthe clinical implications of this finding are that AD may be associated with autonomic disturbances, but patients with AD may rarely report symptoms of autonomic dysfunction. Future research should systematically evaluate symptoms of autonomic function and characterize risk factors associated with autonomic dysfunction.