Objective: Periodic limb movement disorder (PLMD) and obstructive sleep apnea (OSA) are prevalent sleep disorders in Sulfur Mustard (SM) patients. This study aimed to consider the relationship between PLMD frequency and arousal related to PLMD in SM-exposed and OSA patients before and after treatment with continuous positive airway pressure (CPAP). Methods: In this descriptive analytic study, SM-exposed male cases (n=64) with an age-matched group and OSA unexposed controls (n=64) were enrolled. OSA severity based on apnea hypopnea index (AHI), PLMI and PLM-arousal-index (PLMAI) was monitored between two groups in baseline and after CPAP or BiPAP treatment. Results: PLMD frequency in OSA and SM groups was 91.5% and 95.5%, respectively. In SM patients, there were statistical differences for PLMA (p = 0.01), PLMAI (p = 0.02), PLMS associated with respiratory events (p = 0.041), and PLMS without arousal and respiratory events (p = 0.001) after CPAP therapy. But in OSA group, PLMS index (p = 0.003), PLMS associated with respiratory events (p = 0.001), PLMS without arousal and respiratory events (p = 0.001) were significantly different after CPAP therapy. After receiving CPAP, sleep quality in both groups was increased significantly (SM: P = 0.006, OSA: P = 0.001). There were no significant differences between two groups. Conclusion: This study demonstrated that PLMD in SM patients was high and CPAP therapy reduced all these events significantly. This may represent a protective and maintenance Treatment against sleeprelated breathing disorders in SM-exposed patients.