This report describes 7 patients, aged 30 to 43 years, suffering from a mild variant of Sanfilippo B-disease. Somatic findings in these patients are unremarkable. Dementia and behavioral disturbances occurred late in the course of the disease. All 7 patients were examined 10 years previous to this study and reported in earlier publications [van de Kamp et al, 1976, 1981].