Sleep abnormalities are common in patients with asthma and chronic obstructive pulmonary disease. Recent studies have provided new insight into the mechanisms involved in circadian changes in airway resistance, analyzed the effect of disease treatment on sleep quality, and re-examined issues relating to oxygen supplementation at night in patients with chronic obstructive pulmonary disease. Although providing new and useful information, some of these studies also raise new questions that will need answering in the future. This article reviews our current understanding of the complex interactions between sleep and lung disease in patients with asthma and chronic obstructive pulmonary disease.