Extensive and unusual patterns of birth defects noted in four children included defects of the brain, eyes, ears, palate, teeth, heart, feet, nipples, and genitalia. Brain defects were present in the ventricles, corpus callosum, choroid plexus, and septum pellucidum, and genital defects included the testes (undescended), microphallus, and labia (fused). All children had growth retardation, and three had hypotonia and profound mental retardation. The children were exposed in utero to chlorpyrifos (Dursban). Published literature and unpublished documents by the U.S. Environmental Protection Agency contain reports that identify similarities in defects found in test animals and in children exposed to Dursban. A pattern of defects found in the four children in this study may represent a heretofore unrecognized syndrome that should be considered when Dursban-exposed women have children with birth defects.