The reliability and validity of a screening test called the D-CAT (Digit Cancellation Test) were evaluated across two studies. The D-CAT was developed to provide a highly practical and user-friendly assessment of various aspects of prefrontal cortex functioning, including information processing speed, the ability to focus attention, and executive functioning. Participants perform the D-CAT by deleting given target numbers on a sheet of randomly arranged possibilities. In Study 1, the reliability of the D-CAT was evaluated using a test-retest paradigm. Reasonably high correlations between scores on the two test sessions were obtained. In Study 2, construct validity was examined using a sample of participants with traumatic brain injury. TBI participants showed significantly lower D-CAT performance than age and education level matched healthy controls. On the basis of these findings, the D-CAT can be regarded as a reliable and valid screening test for attentional functioning.