Objective: A previous factor analysis of the Conners' Continuous Performance Test (CCPT) indicates that the test measures 5 sub-functions of attention, namely "focused attention," "hyperactivity/impulsivity," "sustained attention," "vigilance," and "change in control." The present study further analyzes the results from Egeland & Kowalik-Gran to test the construct- and criterion-validity of these factors. Method: Construct validity is tested by analyzing whether clinical groups known to be impaired in specified subprocesses actually differ with regard to factor scores. Comparison of CCPT factor scores from 282 individuals with ADHD, schizophrenia, affective disorders, brain injury, language disorders, and normal individuals gives validity to 4 factors, but not to the "vigilance" factor. Results: Other tests of controlled attention correlate only with focused attention, thus giving criterion validity to this factor and differential validity to the remaining 4 factors. Conclusion: Grouping scores on the CCPT into 4 or 5 sub-functions of attention may provide the clinician with a tool to differentiate between clinical groups. (Contains 1 figure and 4 tables.)