 The purpose of this double blind study is to determine whether CERE-120 adeno-associated virus serotype 2 AAV2-neurturin NTN is effective and safe in the treatment of patients with idiopathic Parkinsons Disease. CERE-120 is administered via bilateral stereotactic injections targeting the putaminal region of the brain. The design of this study involves approximately 34 patients receiving CERE-120 treatment via stereotactic surgery and approximately 17 patients receiving sham stereotactic surgery no CERE-120 administered. 