INTRODUCTION: We assessed the effect of periodic leg movements (PLMs) on sleep architecture in narcolepsy patients by comparing sleep patterns in narcoleptics of comparable age with and without PLMs. METHODS: Patients diagnosed with narcolepsy between January 1999 and December 2005 were divided into those with PLM index >or= 5/hr and <5/hr. Each patient underwent polysomnographic recording followed by a multiple sleep latency test (MSLT). RESULTS: There were 47 patients, of mean age 28.9 +/- 1.8 years, 31 (66%) with PLM index >or= 5/hr and 16 (34%) with PLM index <5/hr. Arousal index, PLM arousals and total number of arousals were all significantly higher in narcoleptics with PLM index >or= 5/hr than in those with PLM index <5/hr. Significant correlations were found between PLM index and arousal index, stage shifts, Stage 1 and average sleep latency on MSLT. CONCLUSIONS: Our findings demonstrated that narcolepsy patients with PLMs have a higher arousal index and increased PLM arousals compared with narcolepsy patients without PLMs. The contribution of the above to the perceived sleep quality and daytime sleepiness is not clear