Objective/Method: The Conner's Continuous Performance Test (CPT) was administered to four groups of adult college students who self-referred for comprehensive psychoeducational evaluation and received either no diagnosis (n = 30) or a diagnosis of ADHD (n = 26), a psychiatric disorder (n = 17), or various cognitive deficits (n = 22). Results: The groups did not differ with respect to age, sex, race, or IQ. Although the ADHD group made more CPT errors of omission, had longer response times, and showed greater variability in responding than the other three groups, these differences did not reach statistical significance when analyzed parametrically using standard scores. But when the pattern of scores across the groups was analyzed nonparametrically, significant and interpretable results emerged. Conclusion: The CPT reliably differentiated between individuals with ADHD and both normal college students and individuals with psychiatric diagnoses but not persons with learning/cognitive disorders. (Contains 2 tables.)