Prior research has shown that individuals with obstructive lung disease are at risk for sleep fragmentation and poor sleep quality. We postulated that patients with chronic obstructive pulmonary disease (COPD) and obstructive sleep apnea (known as overlap syndrome) who have more severe lung disease, as measured by lung hyperinflation (inspiratory capacity/total lung capacity), would have greater sleep disturbances independent of traditional measures of sleep apnea. We performed a retrospective chart review of consecutive patients evaluated and treated in an academic pulmonary clinic for overlap syndrome. Pulmonary function tests and polysomnogram data were collected. Thirty patients with overlap syndrome were included in the analysis. We found significant univariable associations between sleep efficiency and apnea/hypopnea index (beta = -0.285, p = 0.01) and between sleep efficiency and lung hyperinflation (beta = 0.654, p = 0.03). Using multivariable linear regression, the relationship between sleep efficiency and lung hyperinflation remained significant (beta = 1.13, p = 0.02) after adjusting for age, sex, body mass index, apnea/hypopnea index, FEV(1)% predicted, oxygen saturation nadir, medications, and cardiac disease. We conclude that increased severity of hyperinflation is associated with worse sleep efficiency, independent of apnea and nocturnal hypoxemia. The mechanisms underlying this observation are uncertain. We speculate that therapies aimed at reducing lung hyperinflation may improve sleep quality in patients with overlap syndrome.