It has been suggested that performance on the Wisconsin Card Sorting Test (WCST) may be an indicator of vulnerability to schizophrenia. WCST deficits have been demonstrated in schizophrenic patients and their relatives, but not as yet in their offspring. This study aimed to further establish the indicator potential of WCST deficits by analyzing data collected as part of the New York High-Risk Project (NYHRP), a longitudinal study of attention, cognition and clinical functioning in the offspring of schizophrenic (HRSz, n=73), affective disordered (HRAff, n=61) and normal comparison (NC, n=120) parents. Parental Research Diagnostic Criteria diagnoses were established by semi-structured interview (SADS-L). WCST testing was carried out when offspring were in their mid-20s. HRSz subjects performed significantly more poorly on the WCST than HRAff and NC subjects. High-risk subjects who developed psychotic symptoms prior to or shortly after testing did not differ significantly from HRSz subjects who did not become ill. Thus, WCST performance in the offspring of schizophrenics resembles that of schizophrenic patients and may distinguish HRSz from offspring at risk for nonschizophrenic illness. WCST deficits may be a specific familial indicator of vulnerability, but appear not to distinguish between those subjects at risk for schizophrenia who do or do not become ill.