A wide ranging survey was carried out of the available data from ten different countries on human exposure to chlorpyrifos, in many different occupational and nonoccupational settings. Low levels of chlorpyrifos residues were found to be widely distributed in the global human population, but most of these do not constitute a public health risk, as evaluated using the U.S. Environmental Protection Agency (USEPA) Guidelines. For example, the general populations in USA, Germany and Italy had detectable residue levels well below the guidelines. However, high levels of health risk were apparent in a specific group of pregnant mothers in the USA, at median exposure with a HQ0.50 of 26.6, suggesting that most of this population group was affected. Also the high exposure group (5% most exposed) with occupationally exposed manufacturing workers in the USA had a HQ0.95 of 2.6 to 42.0, and pest control applicators in Australia and the USA both had a HQ0.95 of 5.2. Some farmers in Sri Lanka and Vietnam had a high level of risk after spraying applications, having a HQ0.95 of 2.2 and 19.5 respectively at the high exposure level. These results suggest that there is a possibility of adverse health effects in specific population groups in many different settings throughout the world.