Aim: An imbalance between T-helper type 1 (Th1) and type 2 (Th2) cytokines has been implicated in schizophrenia, although empirical evidence is rare. The aim of this study was to examine if a Th1/Th2 imbalance occurs in schizophrenia and schizophrenia-related disorder.Methods: Twenty-six subjects with schizophrenia, 26 subjects with schizophrenia-related disorders, and 26 healthy controls were recruited. The Human Th1/Th2 Cytokine Cytometric Bead Array Kit-II was utilized to assess serum Th1/Th2 cytokines and ratios simultaneously. MANOVA was used to detect differences among the three diagnostic groups in distinct Th1/ Th2 cytokines/ratios. Pearson/Spearman correlations were used to examine the relationships between distinct Th1/Th2 cytokines/ratios and clinical/ psychopathological data in schizophrenia.Results: Interferon (IFN)-g/interleukin (IL)-4, IFN-g/ IL-10, IL-2/IL-4, and tumor necrosis factor (TNF)-a/IL-4 ratios were significantly decreased in schizophrenia, but not in schizophrenia-related disorders compared to healthy controls. IFN-g/IL-4 and IFN-g/ IL-10 in schizophrenia subjects positively correlated with age, but not in schizophrenia-related disorder subjects or in healthy controls. Conclusion:A clear Th2 shift was observed in schizophrenia, but not in schizophrenia-related disorders. The Th2 shift in schizophrenia appeared to be an aberrant developmental phenomenon.