Familial amyloid polyneuropathy (FAP) is a progressive disease. Patisiran is an investigational small interfering RNA (siRNA) targeting TTR. The primary objective of the Phase 2 study is to evaluate the safety of 0.3 mg/kg patisiran administered intravenously once every 3 weeks. Twenty-seven patients were enrolled; the mean duration of treatment was 7 months (range 3–12), with 282 doses administered (median of 11 doses/patient). Chronic dosing with patisiran has been generally well tolerated. Two patients experienced serious adverse events regarded as being unrelated to study drug. Infusion-related reactions were observed in 14.8% of the patients, were mild in severity, and did not result in any discontinuations. Sustained TTR lowering of at least 80% was achieved based on serial TTR measurements for over 9 months, with further nadir of up to 89.6% between doses. Neurologic impairment scores were stable after 6 months of treatment with patisiran. A mean decrease from baseline in mNIS+7 of 0.95 points (N=19) observed in this study compared favorably to the estimated increase of 7–10 points in mNIS+7 at 6 months from prior FAP studies in a patient population with similar baseline NIS values. Dosing continues in all patients, and 12–month results will be presented.