Cleaning of the devices to be sterilized is an essential requisite for the successful outcome of the whole process. The purpose of cleaning is to reduce the amount of microbial contamination by over 90% and to remove the organic material left behind by the preceding procedure. If these remain on the devices they can hinder the action of the sterilizing agent and defeat the whole process. If an instrument is not clean, its sterilization cannot in any way be obtained. But the sterilization process cannot detect if an instrument is “still dirty” and cannot establish that, as such, it is not suitable for being sterilized. Not only that, the checking of the physical parameters of the corresponding cycle can wrongly validate a process that in reality has not been efficacious on the whole load. It is therefore up to the professionalism of the operators to guarantee correct cleaning of the medical device. Cleaning makes use of the chemical action of a detergent, preferably one that is enzyme based and at the same time non-corrosive, which must be used strictly at the concentrations and for the times recommended by the supplier. It is necessary to renew the solution frequently to avoid accumulation of residues that would corrode the devices and reduce the cleaning action. Ultrasonic tanks are the most suitable devices for being sure of a complete removal of organic material and hard materials. The cleaning procedure must be carried out in a dedicated room or space. The cleaning operators must use personal protective equipment (goggles-visors-gloves-aprons).