Periodic limb movements (PLM) cause sleep disorders and daytime symptoms and are frequently associated with restless legs syndrome (RLS). Treatment of RLS with increased PLM during sleep (PLMS) has been evaluated in studies limited in size, methodology and study length. This long-term, placebo-controlled, multi-center, study with polysomnography (PSG) recordings has been designed in order to assess efficacy and safety parameters of pergolide treatment in RLS. This novel approach for a study was created to assure consistently high quality of sleep recording and analysis. Using defined criteria, 21 sleep centers were approved for the study after a pilot phase. Seventeen centers with 16 different PSG systems randomized 100 patients. Digital sleep recordings from 4 visits (baseline, 6 weeks, 6 months, 1 year) were submitted to one central evaluation center following previously defined standardized operating procedures. Visual scoring of all recordings was performed by one independent scorer. Reliability of scoring was evaluated for 20 randomly selected baseline recordings. The mean epoch by epoch agreement for sleep stages was 88% (range 81-96%), mean arousal re-scoring differed by 0.5 (range: -16 to 20), and mean PLM index re-scoring differed by 0.1 (range: -1.5 to 2.1). Using one scorer with a demonstrated high reliability in PSG scoring for all sleep recordings was very effective in terms of study cost, study duration, and data quality.