Nocturnal symptoms and overnight decrements in lung function are a common part of the asthma clinical syndrome. As many as 75% of asthmatic subjects are awakened by asthma symptoms at least once per week, with approximately 40% experiencing nocturnal symptoms on a nightly basis. An extensive body of research has demonstrated that nocturnal symptoms of cough and dyspnea are accompanied by circadian variations in airway inflammation and physiologic variables, including airflow limitation and airways hyperresponsiveness. Alterations in beta2-adrenergic and glucocorticoid receptors and hypothalamic-pituitary-adrenal axis function might play a role in modulating the nocturnal asthma phenotype, and recent studies have suggested that melatonin, a neurohormonal controller of circadian rhythms, might be important as well. Treatment strategies in nocturnal asthma are similar to those used in persistent asthma, although dosing of medications to target optimum effect during periods of nocturnal worsening is beneficial.