CoQ 10 may be helpful in delaying the progression of hearing loss in patients with the 7445A-->G mitochondrial mutation. Objective. To assess the effect of an antioxidant drug (Coenzyme Q-10) on the hearing level of patients with the mitochondrial DNA 7445A-->G mutation and associated sensorineural hearing loss (SNHL). Material and methods. We identified three patients with bilateral non-syndromic SNHL harboring the mitochondrial 7445A-->G mutation. Two patients had a family history of hearing loss with a strong matrilineal inheritance. The other patient did not have a family history of hearing loss. Two patients (1 with familial and 1 with sporadic SNHL) received treatment with 75 mg of Coenzyme Q-10 (CoQ10) twice a day for 1 year. The remaining patient with a familial form of hearing loss did not agree to take the treatment. Average bone conduction pure-tone thresholds for 0.5, 1, 2 and 4 kHz were obtained before and after diagnosis of mitochondrial hearing loss, and before and after treatment with CoQ10. Results. CoQ10-treated patients did not show any additional deterioration of their SNHL after 12 (familial case) and 13 months (sporadic case). The progression rate of SNHL was 6 dB/year in the 2 years prior to initiation of treatment in the familial case who received CoQ10 treatment. One year after being diagnosed with mitochondrial hearing loss, the patient who refused CoQ10 treatment exhibited an 11-dB deterioration of his hearing thresholds. There were no side-effects related to treatment with CoQ10.