The authors investigated the behavioural dimensions of 269 intellectually disabled (ID) people in residential care in specialized institutions in Tolna county (South-West Hungary) with the aim of screening the frequency and severity of the relevant behavioural symptoms associated with intellectual disability and depending on the level of intellectual impairment. Only 120 residents had an International Classification of Disease (ICD) diagnosis of "mental retardation (MR)" and a valid IQ grading either by means of the Hungarian standard version of the HAWIK or by the coloured Raven test. 4 IQ groups were created: borderline (B), mild (MID), moderate (MOD) and profound (PID) intellectual disability subgroups. The Hungarian pilot version of the Behaviour Problem Inventory (BPI) was used. Seventy-two percent of the residents displayed behavioural problems. All scale score means exhibited an enhancing tendency with IQ loss, as both frequency and severity increased linearly towards the more severe groups, but significantly only in the category of stereotyped behaviour. The authors focussed on problems of patient recruitment and discussed the measurement of behavioural and other psychiatric symptoms when researchers reported on the increased occurrence of behaviour and psychiatric symptoms in ID populations. (Contains 1 graph and 2 tables.)