Sanfillippo B syndrome (mucopolysaccharidosis (MPS) III, type B) is characterized by mild expression of the characteristic 'Hurler' phenotype and a severe central nervous system involvement. We report three patients with Sanfilippo B syndrome, referred to our clinic because of peculiar facies, delay in language development and behavioral problems, at the ages of 4, 3 and 5 years, respectively. At presentation they manifested clinical features of MPS, severe developmental retardation, radiological features of dysostosis mutiplex, as well as neurophysiological findings suggestive of carpal tunnel syndrome and sensorineural hearing impairment. Due to marked urinary excretion of heparan sulfate, as well as deficiency of alpha-N-acetylglucosaminidase in leukocytes, the diagnosis of Sanfilippo B syndrome was made. Serial brain magnetic resonance imaging (MRI) at different ages demonstrated white matter abnormalities, cortical atrophy and ventricular enlargement in all three patients, while other findings included thickening of the diploe in two patients and callosal atrophy, basal ganglia involvement, cerebellar changes and dilatation of venous sinuses in one patient. Although the combination of the above MRI findings is highly suggestive of a MPS, they carry a little predictive value in the different clinical stages of MPS IIIB.