Alzheimer's disease (AD) is a central nervous system disorder characterized by the presence of neurofibrillary tangles, neuritic plaques and dystrophic neurones in susceptible areas of the brain. Few options for treatment of AD symptomatology are available. We conducted a multicenter, randomized, double-blind, placebo-controlled, parallel trial consisting of a 90 day treatment period followed by a 30 day single blind placebo administration and by an optional long term period of treatment up to a year with idebenone in open fashion. Ninety two patients entered the study and nine of them dropped out before the first control. Treatment with idebenone was found effective on memory, attention, and orientation and in slowing down the natural progressive worsening of the disease. The most common side effects associated with this treatment were insomnia, gastralgia, nausea, and anxiety. However, all adverse effects were of mild intensity and did not require specific therapies.