We conducted an open, 16-week study on the efficacy of memantine on behavioral disturbances and psychotic symptoms in moderate to moderately severe Alzheimer s disease in daily routine. Fifty-three patients of 20 outpatient centers in Austria were recruited. The Neuropsychiatric Inventory (NPI) was defined as main outcome measure. After 16 weeks the total NPI score improved by 4,6 points (p<0.01). The caregiver distress score was also significantly reduced. The most pronounced improvements were seen in the NPI components depression (-24,6%), aberrant motor behavior (-16,9%), agitation/agression, fear, apathy, disinhibition and disturbances in appetite and eating behavior (-11,3%, each). Our naturalistic study is in line with the results of controlled trials in moderate and severe Alzheimer dementia stages. Controlled clinical trials which have behavioral disturbances and psychotic symptoms as primary endpoint are needed to define the true potential of memantine in mild dementia stages.