Idebenone is a new cerebro-active drug, effective in dementia disorders, particularly indicated in primary degenerative dementias, i.e. Alzheimer's disease. This new molecule acts as an electron trapper and a free radical scavenger protecting mitochondrial membranes from lipid peroxidation. A multicentric, double-blind trial of idebenone (45 mg twice daily orally) vs. placebo was carried out on 102 elderly patients affected by Alzheimer-type dementia of mild or moderate severity. Idebenone was administered for 4 consecutive months, 45 mg twice daily. Clinical evaluations were performed at the time of enrollment (t0) and monthly thereafter (t30, t60, t90 and t120) and at follow-up (t150 ). Tolerability to idebenone treatment was good and was associated with a statistically significant improvement of memory, attention and behaviour. It is worthwhile noting that these cognitive and behavioral findings were observed after the first month of treatment with enhancement evident in the following period.