The paper aims at focusing the relationship between scientific evidence and ethical values' issues of occupational health practice according to the new Italian law 81/2008 stating that the occupational health physician (OHP) is required to act according to the Code of Ethics of the International Commission on Occupational Health. The code itself emphasizes that (i) the practice should be relevant, knowledge-based, sound, and appropriate to the occupational risks and (ii) the objectives and methods of health surveillance must be clearly defined. Because exposure to nanoparticles involves several uncertainties about health effects and may limit the effectiveness of workers' health surveillance, OHPs face a several ethical dilemmas, involving different stakeholders. The dilemmas arising from the practice should be dealt with according to the ethical principles of beneficence, autonomy, and justice in order to take a decision.