This chapter focuses on the three principles for the protection of human subjects of scientific research, established in the Belmont report. These principles include: respect for persons, beneficence, and justice. The principle of beneficence, with the assessment of benefit-risk ratio, poses the most complex issues. A literature search yielded few systematic studies of the physical or psychologic risks of biological research procedures in general, and none on neuroimaging in children. The risks involved in neuroimaging research in children include those associated with radiation exposure, electromagnetic fields, and psychologic stress. The risk of breach of confidentiality between children and parents needs to be carefully evaluated and is particularly salient in research with adolescents. The chapter considers the possibilities for improving the benefit-risk ratio by increasing benefits, decreasing risk, or both. Current regulations may excessively limit children's opportunities both to contribute altruistic service and to benefit as a group from research.