Sterility testing is an important step in verifying that the aseptic process has rendered a preparation sterile. Ensuring sterility involves the oversight and control of many factors, including compounding personnel, pharmacy environment, equipment and materials used in the compounding of sterile preparations, and compounding and aseptic methods. A pharmacy should have a standard operating procedure in place for investigating sterility failures, and an important focus in the procedure should be good documentation. Routine evaluations of a pharmacy's compounding practices should be considered even though such evaluations may present a challenge to the pharmacy's quality control system. Proper training and encouragement of staff to present possible sterility problems could make the difference in avoiding compounding failures.