BACKGROUND: In myotonic dystrophy type 1 (DM1), sleep disorders are common, with excessive daytime sleepiness (EDS) as a predominant feature. In myotonic dystrophy type 2 (DM2), the presence of sleep disturbances is unknown. OBJECTIVE: To investigate the frequency of EDS, poor sleep quality and fatigue in DM2. METHODS: 29 genetically proven DM2 patients were surveyed using the Epworth Sleepiness Scale, Pittsburgh Sleep Quality Index (PSQI) and Checklist Individual Strength. The results were compared with 29 adult onset DM1 patients and 65 population controls, both matched for age and sex. RESULTS: Only 6.9% of DM2 patients had EDS compared with 44.8% of DM1 patients and 6.2% of population controls (DM2-DM1: p=0.001; DM2-controls: p=0.51). Sleep quality was poor (PSQI >5) in both DM2 and DM1 groups, and differed significantly from population controls (DM2 6.5+/-3.0; DM1 6.2+/-3.7; controls 4.3+/-3.0; DM2-controls: p=0.002). Poor sleep quality was not explained by depression or other comorbidity but was mainly due to sleep disturbances as a result of nocturnal pain. Comparable with the DM1 group, DM2 patients experienced severe fatigue (DM2 38.7+/-13.1; DM1 42.9+/-8.5; controls 21.1+/-11.1; DM2-controls: p