An echocardiographic study was realized in four patients with the Hunter syndrome (mucopolysaccharidoses II), evidenced by the clinical, radiologic and laboratory data. Mitral incompetence was present in two of the cases. In cases without mitral incompetence the echocardiographic tracing showed multiple mitral systolic echoes with a normal left atrium. On the other hand in cases with mitral incompetence the echocardiograms showed multiple systolic and diastolic echoes of the mitral valve with left atrial enlargement.