Association with schizophrenia of the Abelson Helper Integration Site 1 (AHI1) gene on chromosome 6q23 and the adjacent primate-specific gene, C6orf217, was demonstrated in an inbred, Arab Israeli family sample and replicated in an Icelandic case control sample. Further support was provided by a second replication in a large European sample and a meta-analysis that supported association with schizophrenia of all seven alleles overtransmitted to affected subjects in the original study. We examined constitutive expression of AHI1 and C6orf217 in immortalized lymphoblasts of patients from the Arab Israeli family sample in which the association with schizophrenia was originally discovered and population-matched normal controls, and in post-mortem brain of patients with schizophrenia and bipolar (BP) disorder and control subjects from the Stanley Medical Research Institute Collection. We found a significant effect of diagnostic group in the lymphoblast sample (F=5.72; df=2,39; p=0.006). Patients with early age of onset had higher AHI1 expression than controls and later onset patients (p=0.002; 0.03 respectively). C6orf217 expression in lymphoblasts was too low to measure. We found no difference in brain expression of AHI1 in schizophrenia or BP patients compared to controls. However, there was a genotypic difference in AHI1 expression for SNP rs9321501, which was strongly associated with schizophrenia in the original study. Genotypes that included the undertransmitted C allele (CC/AC) showed lower expression than the homozygous AA genotype (F=4.73, df=2,83; p=0.028). There was no significant difference in brain expression of C6orf217 between patients and controls and no genotypic effect. This study provides further evidence for involvement of AHI1 in susceptibility to schizophrenia.