This study investigated the influence of 'cognitive busyness' (competing cognitive demands) on residential care staff attributions of challenging behaviour (CB) related to dementia. Following the model of attribution formation proposed by Gilbert, Pelham, and Krull (1988), it was hypothesised that care staff experiencing competing cognitive demands at the time of observing CBs linked with dementia would be more likely to make internal and controllable attributions regarding the causes of such behaviour. This study employed a cross-over experimental design. Thirty formal dementia care-workers viewed two video clips of simulated CB, one under conditions of cognitive 'busyness' and another under control conditions of no extra cognitive demands. These conditions occurred a week apart and were counterbalanced, i.e. one group of participants undertook the control condition first and then the experimental condition whilst another undertook the reverse. Self-report measures of attributions were administered after the viewing of each video clip. Competing cognitive demands significantly influenced staff attributions regarding CB, in relation to internality and controllability, and type of CB emerged as a potential moderating factor. No link was found between cognitive busyness and other attributional dimensions (stability and globality). Concurrent cognitive demands seem capable of impairing the ability to use situational information to form some causal attributions regarding CB in dementia but this might depend on the type of CB being witnessed. The results are discussed in relation to key methodological and conceptual issues.