Coenzyme Q-10 (CoQ10) is a widely used alternative medication or dietary supplement and one of its roles is as an antioxidant. It naturally functions as a coenzyme and component of oxidative phosphorylation in mitochondria. Decreased levels have been demonstrated in diseased myocardium and in Parkinson disease. Farnesyl pyrophosphate is a critical intermediate for CoQ10 synthesis and blockage of this step may be important in statin myopathy. Deficiency of CoQ10 also has been associated with encephalomyopathy, severe infantile multisystemic disease, cerebellar ataxia, nephrotic syndrome, and isolated myopathy. Although supplementation with CoQ10 has been reported to be beneficial in treating hypertension, congestive heart failure, statin myopathy, and problems associated with chemotherapy for cancer treatement, this use of CoQ10 as a supplement has not been confirmed in randomized controlled clinical trials. Nevertheless, it appears to be a safe supplementary medication where usage in selected clinical situations may not be inappropriate. This review is an attempt to actualize the available information on CoQ10 and define its potential benefit and appropriate usage.