To help determine whether sustained attention deficits as measured with the Continuous Performance Test (CPT) are stable vulnerability indicators of schizophrenia, we compared the CPT performance of schizophrenic patients before and after treatment with risperidone or haloperidol. In this double blind trial, 56 schizophrenic patients were randomly assigned to a 12-week regimen of either risperidone or haloperidol, after a 1-week washout period. The patients undertook two sessions of the CPT (undegraded and 25% degraded) twice, one at the end of the washout period and the other at the end of the study. Thirty-eight patients completed the study, 19 in each group. Both groups experienced significant improvements in clinical symptoms, and the risperidone group showed no change in the severity of extrapyramidal symptoms. Despite those improvements, the CPT performance indexes did not change significantly from the beginning to the end of the study. These findings indicate that sustained attention deficits might be stable vulnerability indicators of schizophrenia.