Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases in affluent countries. Accurate noninvasive tests for liver injury are urgently needed. The aim of this study was to evaluate the accuracy of transient elastography for the diagnosis of fibrosis and cirrhosis in patients with NAFLD and to study factors associated with discordance between transient elastography and histology. Two hundred forty-six consecutive patients from two ethnic groups had successful liver stiffness measurement and satisfactory liver biopsy specimens. The area under the receiver-operating characteristics curve (AUROC) of transient elastography for F3 or higher and F4 disease was 0.93 and 0.95, respectively, and was significantly higher than that of the aspartate aminotransferase–to–alanine aminotransferase ratio, aspartate aminotransferase–to–platelet ratio index, FIB-4, BARD, and NAFLD fibrosis scores (AUROC ranged from 0.62 to 0.81, P < 0.05 for all comparisons). At a cutoff value of 7.9 kPa, the sensitivity, specificity, and positive and negative predictive values for F3 or greater disease were 91%, 75%, 52%, and 97%, respectively. Liver stiffness was not affected by hepatic steatosis, necroinflammation, or body mass index. Discordance of at least two stages between transient elastography and histology was observed in 33 (13.4%) patients. By multivariate analysis, liver biopsy length less than 20 mm and F0-2 disease were associated with discordance. Conclusion: Transient elastography is accurate in most NAFLD patients. Unsatisfactory liver biopsy specimens rather than transient elastography technique account for most cases of discordance. With high negative predictive value and modest positive predictive value, transient elastography is useful as a screening test to exclude advanced fibrosis. Liver biopsy may be considered in NAFLD patients with liver stiffness of at least 7.9 kPa. (HEPATOLOGY 2010;51:454–462.)