INTRODUCTION: Schizophrenic patients show a significantly higher frequency of hyperbilirubinemia than patients suffering from other psychiatric disorders and the general healthy population. To determine whether patients with schizophrenia-associated idiopathic unconjugated hyperbilirubinemia ( Gilbert's syndrome, GS) have a specific clinical character, various clinical assessments were performed. METHOD: Thirty-three schizophrenic patients with GS and 33 schizophrenic patients without GS were clinically assessed. The symptom profile, level of functioning, and extrapyramidal symptoms were evaluated by means of the Positive and Negative Syndrome Scale (PANSS), Brief Psychiatric Rating Scale (BPRS), Global Assessment of Functioning Scale (GAF), Chouinard Extrapyramidal Symptom Rating Scale (ESRS), Abnormal Involuntary Movement Scale ( AIMS), Drug-Induced Extra-Pyramidal Symptoms Scale ( DIEPSS), and Prins Henrry Hospital Akathisia Scale ( PHAS). RESULTS: In the acute phase, positive and general PANSS scores were significantly higher in schizophrenic patients with GS than without GS. However, there was no difference between schizophrenic subjects with GS and without GS on the negative symptom subscale. Moreover, in evaluation by BPRS and GAF, there was a significant difference between the two groups. In the stable phase, all subscales of PANSS scores were significantly higher in schizophrenic patients with GS than without GS. Similarly, there were significant differences between schizophrenic patients with GS and without GS on the BPRS and GAF. All scores of the rating scale of extrapyramidal symptoms were significantly higher in schizophrenic patients with GS than without GS. CONCLUSION: These findings suggest that there are significant clinical character differences between schizophrenic patients with GS and without GS. From the viewpoint of the heterogeneity of schizophrenia, there may be a poor outcome for the subtype of schizophrenia with GS than without GS.