Mucopolysaccharidosis type VI (MPS VI) is a progressive, autosomal, recessive lysosomal disorder. This disorder, due to a deficiency in N-acetylgalactosamine-4-sulfatase (ASB), results in an accumulation of glycosaminoglycan (GAG), causing multiple organ failures. In this study, monochorionic biamniotic twins with the severe form of MPS VI underwent enzyme replacement therapy (ERT) with weekly infusions of recombinant human ASB (galsulfase) at 1 mg/kg. After 9 years of ERT, a comprehensive clinical examination was performed. Several types of biochemical, immunological, and genetic investigations were also conducted. Both twins showed the typical symptoms and signs of MPS VI at baseline, including short stature, progressive dysmorphic facial features, and dysostosis multiplex. Twin 2 presented stronger multisystemic involvement, with marked musculoskeletal, neurological, and odontological components. She also developed an ischemic spinal cord lesion after surgery, which is the first case described in the literature in Maroteaux-Lamy syndrome. However, the extent of disease was found to be equally stabilized in the two sisters, concretely the cardiac and respiratory functions and body length. The early diagnosis and treatment of MPS VI are critical for an optimal clinical outcome, and further evidence for the new treatment strategies is needed.