OBJECTIVE This study was undertaken to clarify whether idiopathic edema is a marker for obstructive sleep apnea (OSA), independent of level of obesity, in patients with normal left ventricular function. METHODS Seventy-eight ambulatory, obese, adults, 44 with bilateral, pitting pre-tibial edema, and 34 without edema, from an inner city family practice and a suburban family practice enrolled from July 1995 until March 2003. Edematous subjects, but not non-edematous subjects, underwent echocardiography, urinalysis, and blood test evaluations to ensure that cardiac, renal, hepatic, and thyroid functions were normal. All subjects underwent spirometry, pulse oximetry on room air, and polysomnography evaluations. RESULTS Compared to the non-edematous subjects, the edematous subjects were more obese (body mass index=47.0+/-9.3 versus 36.5+/-4.6 kg/m2, P=0.002), had more severe OSA (apnea-hypopnea index (AHI)=34.1+/-27.7 versus 17.0+/-19.4, P=0.002), and had lower oxygen saturations (96.2+/-2.0 versus 97.1+/-1.5%, P=0.05). Using an AHI > or = 15 as the criteria for diagnosing OSA, there was an association between edema and OSA in women (P=0.02) but not men. CONCLUSIONS In subjects with normal left ventricular function, idiopathic edema is associated with OSA in women.