Although the Ontario Society of Occupational Therapists (OSOT) Perceptual Evaluation has been widely used, it has never been standardized. A study was undertaken to examine the validity of the battery for differentiating neurologically normal persons from those who have been independently diagnosed as neurologically impaired. A group of 80 brain-damaged patients was compared with a matched group of 70 neurologically normal persons. Comparison of scores for the two groups supports the validity of the instrument for differentiating the neurologically normal from the perceptually impaired person. The distribution of scores suggests that the degree of impairment can be classified as mild, moderate, or severe. Finally, the OSOT Perceptual Evaluation is found to be a reliable procedure for the assessment of perceptual dysfunction.