A screening of hearing and visual function was performed using clinical assessment methods in a Dutch institutionalized population of 672 people with mild to profound intellectual disability (ID). Because the studied population was not comparable to the total Dutch population with ID, subgroups were distinguished according to level of ID, age younger and older than 50 years, and the presence or absence of Down's syndrome (DS). The prevalences of both hearing and visual impairment were considerably increased in all subgroups, as compared with the general population. In the least affected group, i.e. those < 50 years with a mild or moderate ID by other causes than DS, the prevalences of hearing and visual impairment were 21% and 4%, respectively (as opposed to 2-7% and 0.2-1.9% in the general Dutch population <50 years, respectively). The prevalence of hearing impairment showed a sharp and highly significant increase in individuals with DS and subjects > or = 50 years. To a lesser extent, young adults with severe or profound ID had an increased risk of hearing impairment. Visual impairment and blindness were specifically highly prevalent in people with severe or profound ID (51% < 50 years of age). Down's syndrome and an age > or = 50 years were also significant risk factors for visual impairment. There was an alarmingly high prevalence of combined sensory impairment, especially in those with severe or profound ID (20%). Although hearing impairment had been diagnosed prior to this screen in 138 people and visual impairment in 65 individuals, a first diagnosis of hearing impairment was made in 128 subjects and of visual impairment in 90 cases. This highlights the tendency for sensory impairments to go unnoticed in people with ID, which is not restricted to those with severe or profound ID. Therefore, the present authors stress the importance of regular screening as outlined in the existing IASSID international consensus statement.