This study measures and compares the profit and cost efficiencies of Thai commercial banks between 1990 and 2008 which has been subdivided into the pre-crisis, the financial crisis, and the post-crisis periods. The efficiency scores are measured using a combination of parametric and non-parametric frontier approach. Both average profit and cost efficiency levels of the post-crisis period are found to be significantly lower than those of the pre-crisis period. The evidence also indicates that the real GDP growth rate and some general and financial characteristics are correlated with the efficiency level of Thai commercial banks. of foreign-owned as opposed to domestic-owned banks, and the impact of the financial crisis.Since the 1997 crisis, there have been at least four significant changes in the Thai banking industry, and it is these changes which are the main motivation behind this study. Firstly, the ownership structure has changed dramatically due to the lift of foreign limit control by the Bank of Thailand. This factor affected the ways banks were governed because of the changes incurred by foreign acquisitions and/or domestic mergers. Secondly, the new concept "non-performing-loan (NPL)" was introduced after the crisis. Thirdly, the average capital ratio measured by the equity to total assets decreased from 7.11% before the crisis to 6.58% during the crisis, then increased to 8.72% during the post-crisis period. Finally, the banking industry began taking higher market risks after the crisis causing the percentage of non-interest income to interest income to increase substantially.By taking these factors into consideration, this paper is different from previous studies in several ways. For example, unlike other examinations of the Thai banking system, this paper delivers an updated assessment, which incorporates a much longer duration (1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008) than previous studies. In addition, this paper will measure and compare efficiency levels during the pre-crisis and post-crisis periods. Thus, the full sample period can be divided into three sub-periods for the purpose of comparison: the pre-crisis from 1990 to 1996, the financial crisis from 1997 to 2000, and the post-crisis from 2001 to 2008. Furthermore, this paper is the first to fully utilize an integrated parametric and non-parametric approach in measuring the efficiency levels of Thai commercial banks. That is, cost and profit inefficiency scores are estimated by combining the stochastic frontier approach with data envelopment analysis. It is also important to mention that the inputs and outputs have chosen are based upon Sealey and Lindley (1977), a work which recognizes that the core activity of banks is intermediation.In order to add further detail to our study, possible correlated factors are examined to help explain the difference in average efficiency levels especially between the pre-crisis and post-crisis periods. The generalized least square will b...