Efficacy, safety and tolerability of acetyl-L-carnitine (ALC) were studied during the double-blind placebo-controlled 12-week trial in patients with mild (initial) dementia caused by the Alzheimer's disease (AD) and vascular dementia (VD). ALC was administered in doses from 2250 to 3000 mg per day. Patient's state was assessed with some scales (MMSE, CGI etc) and a battery of neuropsychological tests. The treatment effect of ALC was 2,8 times higher than in placebo-treated patients. The clinical improvement by CGI scores was significantly better in AD patients compared to VD and did not depend on the severity of baseline cognitive deficit. The drug was well-tolerated. Carnicetine can be recommended in the abovementioned doses for treatment of early stages of AD and VD.