It is well known that coenzyme Q10 (CoQ10) has important antioxidant properties. Because one of the main mechanisms involved in the pathogenesis of Alzheimer’s disease (AD) and other neurodegenerative diseases is oxidative stress, analysis of the concentrations of CoQ10 in different tissues of AD patients and with other dementia syndromes and the possible therapeutic role of CoQ10 in AD have been addressed in several studies. We performed a systematic review and a meta-analysis of these studies measuring tissue CoQ10 levels in patients with dementia and controls which showed that, compared with controls, AD patients had similar serum/plasma CoQ10 levels. We also revised the possible therapeutic effects of CoQ10 in experimental models of AD and other dementias (which showed important neuroprotective effects of coenzyme Q10) and in humans with AD, other dementias, and mild cognitive impairment (with inconclusive results). The potential role of CoQ10 treatment in AD and in improving memory in aged rodents shown in experimental models deserves future studies in patients with AD, other causes of dementia, and mild cognitive impairment.