Hunter's disease, a type II mucoplysaccharidosis, a disease of lysosomal overload, may cause cardiovascular disease. This mainly affects the valves of the left heart which are infiltrated, and results in regurgitation rather than stenosis of the aortic and mitral valves. The general context of this disease explains the fact that only one case of mitral valve replacement was found in a review of the literature. The authors report the case of a young patient who was very symptomatic because of mitral and aortic regurgitation and who underwent double valve replacement of the aortic and mitral valves with mechanical prostheses at 18 years of age. The skeletal involvement and respiratory function led to much discussion before surgical referral but the indication was finally retained in view of the patient's practically normal intellectual functions. Seven years later, the patient is asymptomatic from the cardiac point of view and has been included in a protocol of enzyme therapy.