• Change from baseline to end of each treatment period in Periodic Limb Movements associated with Arousal per hour (PLMAI) measured by polysomnography [ Time Frame: 4 weeks ] [ Designated as safety issue: No ]
• Assess safety, tolerability, polysomnography efficacy measures, and patient reported outcomes. [ Time Frame: 4 weeks ] [ Designated as safety issue: No ]

The purpose of this study is to assess the efficacy and safety of GSK1838262 extended release tablets in the treatment of patients with Restless Legs Syndrome and associated sleep disturbance.

• Drug: GSK1838262 Extended Release Tablets
• Drug: Placebo

• Other: GSK1838262 extended release tablets for Treatment Period 1 followed by Placebo for Treatment Period 2
• Other: Placebo for Treatment Period 1 followed by GSK1838262 for Treatment Period 2

Inclusion criteria:

• Provided written informed consent.
• Diagnosed with primary RLS using the International RLS Study Group Diagnostic Criteria with a total score of 15 or greater on the International RLS (IRLS) Rating Scale and significant sleep disturbance indicated on Item 4 of the IRLS rating scale.
• Have history of RLS symptoms at least 15 nights/month.
• Minimum average of 15 Periodic Limb Movements during Sleep per hour (measured using actigraphy).

Exclusion criteria:

• Secondary RLS
• Primary sleep disorder
• Sleep apnea
• Have any medical conditions that may impact efficacy assessments or that may present a safety concern.
• Pregnant or lactating or women of child-bearing potential who are not practicing an acceptable method of birth control.
• Use of any prohibited medication.