This article presents one part of the findings of an ongoing study that set out to investigate and explain the extent of challenging behaviour in twenty-one social service run day and residential services in one large county authority in England. This part of the study reports on staff perceptions of problematic behaviour from service users. It uses staff reports of levels of problematic behaviour as indicative of potentially challenging behaviour. The study uses an adapted version of an established instrument, the BPI (Behaviour Problems Inventory), as a survey tool completed by staff for all service users in a one-month period (January 2000). The findings of this exercise are based on 1,390 service users, near to a census at the time of the survey. The study shows ‘non-compliance’ to be the most problematic and prevalent behaviour from the point of view of staff. Overall the research illustrates a split between the majority of service users who present staff with problematic behaviour in a relatively minor to moderate way and a small group of individuals (less than 2 per cent) who present much more extreme behaviour. Brief reference is made to other data collected in the study when it helps in the interpretation of the behaviour patterns identified by the BPI.