We study the disposition effect in institutional traders by analyzing a unique bond trading dataset of a prominent financial firm in South Korea. The data contains the trade records of RP and Proprietary trading books for the years 2012 and 2013. Overall, Proportion of Gains Realized (PGR) is not meaningfully larger than the Proportion of Losses Realized (PLR) ? that is, there is little evidence of the disposition effect, where the reference is the purchase price, or to alternative specifications. We explain these findings with trader discipline, which mitigates reference dependence and aversion to loss realization. We posit that the results have important implications for market efficiency, since institutional traders play a very important role in the price discovery process of financial markets.