Results of a brief mental status questionnaire, the Cognitive Capacity Screening Examination (CCSE), were compared with the clinical evaluations of 59 patients on a neurology service. In 71% of the cases, the CCSE scores correctly indicated a cognitive deficit (true-positive) or the absence of one (true-negative); false-negative results were observed in 15% and questionable negative results were found in 10%. Abnormal neurologic physical signs were present in 90% of all patients with cognitive deficits. In this population, although positive CCSE scores were reliable, negative scores were often misleading. Mild diffuse intellectual dysfunction (dementia) and some discrete intellectual deficits (aphasia and anosognosia) went undetected. Cognitive deficits associated with major cerebral disease were unappreciated in nine patients. Caution is recommended in interpreting negative CCSE scores. Abbreviated screening devices are only a preliminary approach to mental status evaluation; this test requires further refinement.