One or more ports (34) are formed in a bottom wall (18) of a housing (12) and/or a lid (14) of a medical instrument sterilization container (10). As formed in bottom wall (18), the port (34) includes a circumferential, downwardly tapering side member (42) that extends to a bottom member (40) having a plurality of orifices (44) to communicate a sealed interior (26) with the exterior. A filter cartridge (36) is provided for insertion in the port (34) and has a filter medium (60) that permits the passage of sterilizing gas or steam but does not permit the passage of contaminants. A side member (54) of the cartridge (36) tapers downwardly and inwardly from its perimeter to the filter medium (60) and is adapted to sealingly register with the port side member (42). A retainer (38) may be provided for keeping the cartridge side member (54) in sealing registration with the port side member (42).