Hunter's syndrome is a rare, X-linked recessive, mucopolysaccharidosis. Survival into adulthood is uncommon. Mitral valve disease, predominantly regurgitation, has been reported in these patients. We have found no reports of mitral valve replacement for mitral stenosis secondary to Hunter's syndrome in the English literature. We report that mitral valve replacement for this pathology is a viable treatment option in an adult patient; however, specific precautions must be considered.