Potential adverse health effects associated with exposure to engineered or synthesized nanomaterials have not been reported in humans; however, there is accumulating evidence from animal studies that exposure to some nanomaterials is harmful. While there is uncertainty as to the likelihood, frequency, and intensity of exposures experienced by those working around engineered nanoparticles, this guidance statement was developed for occupational medicine physicians and their colleagues to offer prudent preventive recommendations on the topics of exposure monitoring, exposure controls, and medical surveillance.