The aim of the study was to describe the natural history, anthropometric features, range of motion (ROM) and molecular characteristics of Polish patients with mucopolysaccharidosis (MPS) VI. Clinical heterogeneity was observed and two major clinical phenotypes of the disease were distinguished, rapidly advancing and relatively attenuated. Two patients developed symptoms early in life presenting with short stature, significant skeletal malformations and other clinical abnormalities. In two other patients, height was only slightly decreased and MPS features developed later in the course of the disease. All patients had similar characteristics at the time of birth but showed significant differences in body proportions when compared with the healthy population. Differences between healthy and affected children increased with age and were reflected in phenotypes. Analysis of ROM showed impairments at multiple joints, although to a various degree in different patients. Restriction in upper extremity ROM was observed since the second year of life, while restriction in lower extremity ROM developed later and influenced stereotype of walking. These limitations intensified with the patients’ age, which made self-care more difficult or impossible. The molecular analysis revealed that the milder phenotype may be associated with the R152W mutation, which suggests a specific genotype-phenotype correlation.