Brief neuropsychological tests were administered to an inpatient substance abuse population to (1) evaluate the status of neurocognitive functioning at admission, (2) assess changes that may occur during the treatment program, and (3) compare various testing devices for clinical application in this setting. Patients entering a 14-day inpatient substance abuse unit were tested within a few days of admission with the Neurobehavioral Cognitive Status Examination (NCSE), the Screening test for the Luria-Nebraska Neuropsychological Battery, and the Trail Making Test. Impaired neurocognitive performance was observed in approximately two-thirds of patients; the most frequently compromised areas of functioning involved attention and memory, calculation, abstraction, ability to follow complex commands, and visuospatial skills. Readministration of the NCSE prior to discharge detected a statistically significant improvement in attentional abilities, and a tendency to ward improvement for verbal comprehension and abstraction. Discussion of these findings addresses several issues: (1) the frequency and degree of impairment in this population; (2) the observed variability of cognitive functioning; (3) the question ofclinicalimprovement in neurocognitive functioning observed during a program of this length; and (4) a preference for the NCSE in this setting. The authors argue for the routine neuropsychological assessment of substance abusers, and discuss the above issues in terms of their implications for treatment at both the individual and programmatic level. Discussion of two cases illustrates the application of the NCSE, and the effect of finding organic impairment on staff attitudes and treatment issues.