 Polysomnography PSG will be obtained for two nights of baseline at the end of placebo run-in and at the end of four weeks of treatment with gabapentin encarbil 600 mg. Medical history and cardiovascular risk factors will be assessed at Screening. RLS disease history, previouscurrent RLS therapy, augmentation history and evidence of sleep disturbance will be obtained.Severity of RLS will be determined using the International Restless Legs Syndrome IRLS scale. The Berlin questionnaire will be used to identify the risk low to high of sleep disordered breathing. The Beck Depression Inventory BDI-II will be administered to identify depression and its severity at Screening. Electrocardiogram ECG, clinical laboratory test and urine pregnancy test will be conducted at Screening to determine eligibility. Also to determine eligibility, subjective evidence of sleep disturbance will be assessed per daily sleep diary at Visit 2. A physical exam will be performed at the beginning of the Placebo Run-in Period. 