Visuospatial neglect, a frequent consequence of unilateral (usually right-hemisphere) stroke, is associated with poor functional recovery and in many patients is resistant to remedial treatment. Studies of the nature and prevalence of the disorder have been hindered by problems of definition and assessment. In this study 80 unselected stroke patients were assessed for the presence and severity of neglect on the behavioural inattention test. The six subtests of this battery all intercorrelated highly, and a subsequent factor analysis showed that all tests loaded significantly on one underlying factor. The construct of neglect as defined by performance on the battery is therefore robust. Nonetheless, the individual tests differed substantially in their sensitivity. Star cancellation was the most sensitive measure of neglect and correctly diagnosed all patients whose aggregate score on the full battery fell below that of the control population.