['Obstructive sleep apnea (OSA) is associated with cardiovascular disease through incompletely understood mechanisms. Urinary albumin excretion is a surrogate for endothelial dysfunction and a potent cardiovascular disease risk predictor. We sought to determine whether urinary albumin excretion is increased in subjects with OSA.', 'Four hundred ninety-six adults, representing a spectrum of OSA severity, underwent overnight polysomnography and urine collection. OSA severity was assessed using the apnea-hypopnea index (AHI). The primary outcome measure was the adjusted albumin-to-creatinine ratio (aACR). Linear mixed models were used to assess the association between AHI category and aACR, adjusted for confounders and renal dysfunction.', 'Subjects had a mean age of 44 +/- 17 (SD) years and approximately half were men (44%) and African American (56%). The percentages of subjects with mild (AHI 5-14), moderate (AHI 15-29), and severe (AHI > or = 30) OSA were 23%, 15%, and 15%, respectively. The median aACR for the entire sample was 4.3 mg/g (interquartile range: 2.9, 7.5). Adjusted linear mixed-model analyses showed a significant association between AHI category and aACR, with the AHI > or = 30 group having the highest aACR levels (7.87 +/- 1.02 mg/g vs 5.08 +/- 0.41 mg/g for those with AHI < 5; P < 0.006). Similar findings were observed after excluding subjects with renal dysfunction.'] Is obstructive sleep apnea associated with increased urinary albumin excretion?