A 6-year-old boy suffered acute profound right side deafness after his classmates had mumps. Although his salivary glands were not swollen, he had high levels of anti-mumps IgM and IgG antibodies. The three-dimensional fluid-attenuated inversion recovery (3D-FLAIR) procedure applied to magnetic resonance imaging (MRI) showed high signals in the right cochlea and vestibule. This indicated hemorrhage or a high concentration of protein in the right inner ear. This is the first case demonstrating a high 3D-FLAIR MRI signal of the inner ear in a patient with mumps deafness. Our findings suggest that 3D-FLAIR MRI may help to identify and define labyrinthitis in mumps deafness.