Hepatic steatosis occasionally progresses to nonalcoholic steatohepatitis. This study was designed to examine whether non-obese patients with obstructive sleep apnea-hypopnea syndrome (OSAHS) were prone to develop hepatic steatosis and whether repeated hypoxemia contributed to the progression of steatohepatitis. This study included 83 OSAHS patients and 41 age-, body mass index (BMI)- and gender-matched non-OSAHS patients diagnosed by polysomnography. Hepatic steatosis was defined by a liver/spleen ratio <0.9 on abdominal computerized tomography, and latent steatohepatitis was evaluated based on serum levels of type III procollagen (P-III-P). Visceral fat (V-fat) accumulated much more in OSAHS patients. Liver/spleen ratios in OSAHS patients correlated negatively with BMI and, especially, with the amount of visceral fat. Serum levels of P-III-P in OSAHS patients correlated negatively with the average of oxygen saturation during sleep, and positively with BMI, the apnea-hypopnea index (AHI) and the amount of V-fat. Multiple regression analysis showed that average SaO(2) was the only explanatory variable for P-III-P values, but AHI, BMI and V-fat was not. These observations confirmed that non-obese patients with OSAHS are at a risk for visceral obesity, and suggested that oxygen desaturation during sleep is a risk for developing latent steatohepatitis, especially in patients with substantial hepatic steatosis.