A hot air sterilizer for medical instruments providing rapid sterilization cycle times includes a housing defining a sterilizing chamber. A fan is located in a heated air passage within the housing which extends around the sterilizing chamber from a bottom wall of the chamber to a top wall. The fan circulates air in a closed loop from the top to the bottom of the sterilizing chamber and through the passage. A heater is also located in the passage for heating the circulating air to a temperature sufficiently high for sterilization. Inlet and outlet cooling air passages, separate from the heated air passage, are provided extending through portions of the housing to the chamber. A separate fan, preferably in the inlet passage, circulates air through a portion of the housing along the inlet air passage and through the sterilizing chamber while bypassing the heated air passage and the heater and hot air circulating fan in that passage. Guide rails in the sterilizing chamber uniformly space removable racks each capable of supporting several hinged instruments and several other elongated instruments. The racks are self-supporting and may be removed for chairside use.