Treatment of sleep apnea can improve liver enzyme abnormalities in patients with nonalcoholic fatty liver disease. However, the effect of continuous positive airway pressure therapy for sleep apnea on liver fat accumulation was not assessed. Liver biopsy is the "gold standard" for determining and quantifying liver fat accumulation; however, obtaining two separate liver biopsies is challenging. We examined, using a newly described computerized tomography method to quantify liver fat accumulation, whether treatment of sleep apnea improves liver steatosis. In a prospective cohort study, patients diagnosed with obstructive sleep apnea, at Assaf Harofeh Medical Center's sleep laboratory, were identified. Patients completed a questionnaire and underwent blood tests for liver enzymes and lipid profile, and computed tomography scans to determine the liver attenuation index. Patients with liver attenuation index <or=-10 (correlating with histological macrovesicular steatosis >or=30%) were treated with continuous positive airway pressure for 2-3 years. Subsequently, patients underwent repeat blood tests and tomography scans. Of 47 patients who were analyzed, 16 had a low liver attenuation index (<or=-10). Patients with moderate-severe sleep apnea had worse liver attenuation index compared with patients with mild sleep apnea despite comparable body mass index and triglycerides levels. Patients who were compliant with 2-3 years of continuous positive airway pressure treatment demonstrated significant improvement in the mean liver attenuation index, whereas noncompliant patients did not. Patients with nonalcoholic fatty-liver disease may benefit from identification and treatment for obstructive sleep apnea because treatment may improve liver steatosis.