This study compared the frequency with which unilateral and bilateral cerebral disease gives rise to right sided visual hemispatial inattention. A retrospective survey identified brain injured patients for whom target omissions on visual target cancellation tasks significantly exceeded control values. Subjects consisted of 40 right handed patients referred for clinical evaluation or research study of hemispatial inattention. Right sided visual hemispatial inattention occurred with greater frequency and severity in patients with bilateral lesions than in patients with unilateral left sided or right sided lesions. All eight patients with bilateral lesions manifested right sided hemispatial inattention and failed to detect more targets overall than patients in the other two groups. Of the 13 patients with left sided lesion, seven ignored more targets on the right and six ignored more targets on the left. All but one of the 19 patients with right sided lesions ignored more targets on the left. The association of severe right sided visual hemispatial inattention with bilateral cerebral disease extends previous findings and showed that, in this sample, the most common setting for right sided hemispatial neglect occurred in patients with bilateral cerebral lesions.