There is much evidence to indicate that the dopamine receptor D4 (DRD4) gene is involved in psychiatric disorders. We investigated the correlation between DRD4 gene polymorphism and the psychopathology of major psychoses, independently of diagnoses. Some 461 inpatients affected by major psychoses were assessed by the Operational Criteria checklist for psychotic illness and typed for DRD4 variants. The four symptomatologic factors-mania, depression, delusion, and disorganization-were used as phenotype definitions. DRD4 Exon 3 long allele variants were associated with high delusional scores, with the most significant difference between alleles 2 and 7 (p = 0.004). DRD4 variants may, therefore, constitute a liability factor for development of delusional symptomatology in patients with major psychoses.