Nocturnal asthma is a significant clinical problem in asthmatics that can lead to sleep disruption, daytime fatigue and hypersomnolence. There is increased sleep latency, reduced sleep efficiency and reduction in slow wave sleep. Circadian changes in airway lumen are exaggerated in nocturnal asthma. Hormonal variations at night, increased airway hyperreactivity with inflammation, decreased lung volume and increased intrathoracic blood volume contribute to the pathophysiology. Nocturnal asthmatics demonstrate a reduction in glucocorticoid receptor binding affinity at night as well as an increase in the glucocorticoid receptor splice variant which reduces the efficacy of steroids. Both the number and physiologic function of beta-2 receptors are significantly decreased from 4 PM to 4 AM in asthmatics with nocturnal worsening compared to non-nocturnal asthmatics and normal controls. Chronotherapeutically administered steroids may have an additional role in control of nocturnal asthma. There is a high prevalence of OSA in patients with asthma. This appears to be bidirectional relationship. Females are affected with both concomitantly more often than males. OSA augments asthmatic inflammation at night. Treatment with CPAP improves asthma control without affecting lung functions or airway hyperreactivity.