The purpose of this study was to determine the frequency of obstructive sleep apnea in patients with inflammatory myopathy. An observational and prospective study was performed on a cohort of adult patients with inflammatory myopathy followed at a specialized outpatient clinic. Sixteen consecutive adult patients were evaluated by the Epworth Sleepiness Scale (ESS) and by complete polysomnography study. Disease activity and severity were assessed using the Myositis Disease Activity Assessment Tool (MDAAT) and Myositis Damage Index (MDI), respectively. Associations between sleep parameters and other factors were calculated using the chi-square test, Fisher's exact test, Mann-Whitney U-test, and Wilcoxon's test. A serum autoantibody profile was determined for all patients. The mean apnea-hypopnea index was 28.7 (23.8), and 14 patients (87%) had an apnea-hypopnea index >5. The mean frequency of respiratory arousals was 20.1 (12.5). Eleven (68%) patients reported frequently-always snoring, and 3 (19%) had excessive daytime sleepiness (ESS >10). Seven patients were offered continuous positive airway pressure (CPAP) therapy; 4 tolerated the procedure well and reported a clear improvement in daytime sleepiness and/or sleep quality. No significant association was observed between the apnea-hypopnea index and clinical or immunological groups. Dysphagia, disease activity, and disease severity were not significantly associated with any sleep parameters. The frequency of obstructive sleep apnea in adult patients with inflammatory myopathy is high. The possibility that these alterations play a role in persistent fatigue in these patients cannot be ruled out.