Nonalcoholic fatty liver disease (NAFLD) is a term often used to describe two related conditions: a relatively benign, nonalcoholic fatty liver (NAFL) and potentially aggressive, nonalcoholic steatohepatitis (NASH). Both conditions (NAFL and NASH) occur in the setting of peripheral insulin resistance. Recently, obstructive sleep apnea (OSA) has been proposed as an independent risk factor for insulin resistance. To date, few studies have documented the prevalence of OSA or symptoms of OSA (SOSA) in NAFLD patients. The objectives of this study were (1) to document the prevalence of SOSA in patients with NAFLD and (2) to determine whether prevalence rates for SOSA differ in NAFL versus NASH patients. One hundred ninety biochemically defined NAFLD patients (116 NAFL and 74 NASH), of whom 50 (18 NAFL and 32 NASH) had undergone liver biopsy, completed a Modified Berlin Sleep Apnea Questionnaire for SOSA. Risk factors for NAFLD were also documented in NAFL and NASH patients. Eighty-seven of the 190 (46%) NAFLD patients met questionnaire criteria for SOSA. The prevalence of SOSA was similar in both biochemically (45% versus 49%, respectively; P = 0.66) and histologically (39% versus 63%, respectively; P = 0.11) defined NAFL and NASH patients. Other risk factors for NAFLD such as body mass index, plasma cholesterol and triglyceride levels, and prevalence of diabetes were also similar in the two groups. Approximately one-half of NAFLD patients, whether NAFL or NASH, have SOSA. Further studies are required to determine whether a causal link exists between NAFLD and OSA.