Recent studies indicate that urbanization is having a pronounced effect on disease patterns in developing countries. To understand the immunological basis of this, we examined mRNA expression in whole blood of genes involved in immune activation and regulation in 151 children aged 5-13 years attending rural, urban low socioeconomic status (SES) and urban high-SES schools in Ghana. Samples were also collected to detect helminth and malaria infections. Marked differences in gene expression were observed between the rural and urban areas as well as within the urban area. The expression of both interleukin (IL)-10 and programmed cell death protein 1 increased significantly across the schools from urban high SES to urban low SES to rural (P-trend <0.001). Although IL-10 gene expression was significantly elevated in the rural compared with the urban schools (P<0.001), this was not associated with parasitic infection. Significant differences in the expression of toll-like receptors (TLRs) and their signaling genes were seen between the two urban schools. Genetic differences could not fully account for the gene expression profiles in the different groups as shown by analysis of IL-10, TLR-2 and TLR-4 gene polymorphisms. Immune gene expression patterns are strongly influenced by environmental determinants and may underlie the effects of urbanization seen on health outcomes.