Whether to suggest enrollment of pediatric oncology patients with advanced or refractory disease into a Phase I clinical trial may present a significant ethical dilemma for health care professionals. Phase I trials are experimental and unpredictable by nature, yet health care professionals must ensure the trial's therapeutic intent as well as address the many vulnerabilities of the child with terminal cancer. After reviewing the role and phases of clinical research in pediatric oncology, this article discusses ethical considerations in Phase I clinical trials according to The Belmont Report: Ethical Principles and Guidelines for the Protection of Human Subjects in Research and discusses specific applications of these key ethical principles.