The International Ultraviolet Explorer (IUE) is a large astronomical observatory which was launched on January 26, 1978. The observatory was placed into a three-axis stabilized, eccentric synchronous orbit with an inclination of about 29 degrees. Although it was designed for a 3-year lifetime, it is currently still operational. This paper will briefly review the thermal design which consists of multilayer insulation, ammonia-filled grooved heat pipes, bimetallic actuated louvers, and assorted commandable heaters. It will discuss the 15 years of thermal data and compare the results with prelaunch predictions. This paper will also briefly discuss the more significant flight anomalies. Finally, an attempt will be made to discuss any anomalous thermal behavior with an emphasis on the temperature increase of the hydrazine auxiliary propulsion system.