The United Network for Organ Sharing is planning to resolve the ever-growing geographic disparities in kidney transplantation. Currently available simulation techniques are limited in their ability to analyze the impact of policy changes at the system level. This paper discusses the development of a discrete event simulation of the kidney transplantation system, KSIM. KSIM design is discussed and can easily be adapted to test alternative geographic organ allocation policies. Input analysis employing actual transplantation system data was conducted to best represent patient and organ arrival processes. After discussing our model, we briefly describe how KSIM was verified and validated against twenty years of actual transplantation system information. We also describe the potential usability of KSIM in organ allocation policy development.