Idebenone is a benzoquinone compound which has been investigated in elderly patients with dementia. Its precise mechanism(s) of action remains unknown, but in vitro and in vivo studies suggest the drug may diminish nerve cell damage due to ischaemia, correct neurotransmitter defects and/or cerebral metabolism and facilitate memory and learning. In the small number of studies available for evaluation, idebenone was generally superior to placebo and comparable with bifemelane, oxiracetam and nebracetam on the basis of a number of objective and subjective tests and rating scales in patients with mild to moderate cognitive decline. Clinical trial results indicate that patients with mild dementia seem more likely to respond than those with greater functional decline. The degree of benefit conferred by idebenone is often difficult to determine, but in those who respond, improvement is generally mild to moderate. Therapy with idebenone appears well tolerated for up to 2 years, and no changes in vital signs or laboratory values have been seen in clinical trials. In view of the lack of a proven agent to limit or halt the progression of dementia in the elderly, idebenone may warrant consideration in patients with mild cognitive dysfunction on the basis of preliminary evidence of predominantly mild improvement of functional status in some patients and good tolerability. However, further well designed studies, including comparisons with newer and commonly used agents, such as tacrine, are required to better define the role of idebenone in this complex area of treatment.