Blood will be sampled for an essential fatty acid profile and lipid panel before beginning Omegaven, weekly while the patient is on Omegaven and has a direct (conjugated) bilirubin ≥ 2 mg/dL, and then monthly while the patient is on Omegaven and has a direct (conjugated) bilirubin < 2 mg/dL. Subjects will also be monitored daily for clinical signs and symptoms of essential fatty acid deficiency, including dermatitis and hair loss.