This article examines functions of dietitians who provide nutrition services to patients with inherited metabolic disorders. A survey questionnaire was developed and pilot-tested in a sample of dietitians, revised, and mailed to all dietitians in the United States who treat patients with inherited metabolic disorders. One hundred forty-two usable questionnaires were returned. Descriptive statistics were used to calculate response frequency. The highest academic degree attained by 37% of the dietitians was a bachelor's degree; 58% had earned a master's degree and 5% a doctorate. Dietitians provided nutrition services during diagnosis, critical illness, and long-term care. More than 90% of the dietitians performed these functions: evaluated nutrition status; prepared, implemented, and evaluated the nutritional support plan; revised the nutrition support plan as needed; monitored dietary compliance; coordinated care with other agencies; developed materials and educated parents, caregivers, and patients about the nutrition support plan; and recorded information in the medical record. Without nutrition support, patients with inherited metabolic disorders may become mentally retarded, experience neurologic or metabolic crises, or die.