In an effort to develop standards for the treatment of patients with urea cycle disorders, a consensus conference was held in Washington, DC, from April 27-29, 2000. Conference participants included physicians, scientists, nurses, dieticians, and a genetic counselor, all experts in their various medical fields in these diseases. Representatives from the Food and Drug Administration and the National Urea Cycle Disorders Foundation, a parents support group, also participated in the conference. The goals set forth for the conference were to (1) reach a consensus on diagnostic and therapeutic guidelines for urea cycle disorders with the most up-to-date information and the experience of experts in the field, (2) establish a collaborative network of health care professionals to advance the cause of patients with urea cycle disorders in the areas of clinical management and research, and (3) provide help to health care providers in the recognition and management of these complex disorders by publishing the proceedings of the conference in a widely read journal. The articles that follow this introduction represent the current state of knowledge on the topics addressed in the conference and a summary of the discussions that followed each of the presentations. With input from all the participants, we tried to cover those topics that were believed to be the most relevant both to the experts and to patients. As the reader will appreciate, many unresolved and controversial issues pertaining to treatment have yet to be studied by rigorous scientific methods. On the other hand, there are many issues on which the panel agreed. In many instances the availability of reliable information on the respective topics determined whether consensus could be reached.