Enhanced MRI has recently become an even more useful diagnostic tool in the study of the labyrinth in sudden deafness and vertigo. A 22-year-old male who experienced a right-sided sudden deafness and vertigo due to mumps virus underwent labyrinthine MRI examination with gadolinium, and both labyrinthine and nerve bundle involvement was demonstrated. The relationship between mumps virus and the sudden deafness in humans has not been completely established and the path of labyrinthine infection and the possible eighth-nerve involvement is discussed. In vivo evidence of labyrinthine and cochleovestibular-nerve involvement in mumps virus sudden deafness and vertigo has not been previously demonstrated. MRI findings may represent a new contribution in the evaluation of the etiopathogenesis of mumps virus deafness and vertigo.