The differentiation of the human brain is triggered by sexual steroid hormones in the fetus. The development of both the urogenital system and the appendicular skeleton are under common control by the HOX genes. Generally men have longer ring fingers than index fingers, whereas in women these fingers are close to equal. The inborn digit pattern may reflect fetal estrogen/androgen influences on hemispheric brain specialization. Reduced hemispheric asymmetry has been found in schizophrenia. Gender differences in schizophrenia also suggest a possible endocrine component in the complex pathogenesis of the illness. To test this hypothesis the authors have measured the relative digit lengths of patients with schizophrenia and healthy comparison subjects. The distance of the tip of the index and ring finger was measured from the tip of the third digit in 80 male and 80 female, right-handed patients with DSM-IV diagnosis of schizophrenia and in 80 right-handed healthy comparison men and women. Schizophrenic men and women showed a more "feminine" phenotype of the index and ring fingers in both hands than same-sex controls. This finding implies that low fetal androgen/estrogen ratio may have a predisposing role in the development of schizophrenia and points toward involvement of endocrine factors in the disturbed hemispheric lateralization attributed to the illness.