We present a child with complete biotinidase deficiency who developed bilateral sensorineural deafness without a response to a maximal stimulus of 90 dB in brainstem acoustic-evoked response. After treatment with 20 mg biotin daily, a repeated brainstem acoustic-evoked response demonstrated an improved hearing threshold of 65 dB, and the child began to talk. The case is a rare example of reversible hearing loss caused by to biotinidase deficiency and highlights the need for immediate replacement therapy once the diagnosis is established.