The aim of our study is to demonstrate a causal link between two distinct diagnoses, the hereditary hearing loss, and the sudden sensorineural hearing loss.Sudden sensorineural hearing loss is an emergency condition in otolaryngology and a rare diagnosis in childhood. Most often it only affects one ear and its cause remains unknown.We present a clinical study of a 10-year-old female patient presenting with bilateral sudden sensorineural hearing loss analyzed by Sanger sequencing of the GJB2 gene.The subject was referred to the hospital for bilateral sudden hearing loss which developed 3 days before the admission. Audiometric testing confirmed bilateral asymmetric sensorineural hearing loss. All routine diagnostic procedures including MRI and CT imaging showed normal results. She was treated with intravenous and intratympanic corticosteroids followed by hyperbaric oxygen therapy with partial hearing recovery in one ear. DNA analysis of the GJB2 gene identified biallelic c.35delG deletion. The subject had no other affected family members and her auditory development to that time was normal.Our finding extends the knowledge on phenotype variability in GJB2 variants. We suggest considering genetic testing in pediatric cases of bilateral sudden sensorineural hearing loss (Tab. 1, Fig. 4, Ref. 24).