Type I hyperlipoproteinemia (T1HLP, also known as familial chylomicronemia syndrome or FCS) is a rare diseasewhere the blood triglycerides (fats) are very high. It is caused by lack of certain enzymes and proteins in the bodythat are important in disposing circulating fats from blood. Treatment of T1HLP patients who have very high levels of blood fats (≥ 1,000 mg/dL) is challenging as conventional triglyceride-lowering medications, such as fibrates and fishoil, are ineffective. The purpose of this trial is to study the long-term efficacy and safety of orlistat for reducing blood triglyceride levels in patients with T1HLP.