Abstract: There is disclosed a drainage system for body fluids comprising a catheter having a distal segment adapted to be inserted within the body of a patient and a proximal segment arranged outside the patient's body, a plurality of openings for the passage of fluids from outside the catheter to inside the catheter, a catheter spacing device from the patient's tissues, comprising an expandable balloon arranged helixwise about the distal segment laterally with respect to the openings. The catheter defines, on the external surface, a groove adapted to at least partially accommodate the expandable balloon. There is also disclosed a fastening device for a drainage system comprising a fastening element forming a through-seat for inserting the catheter and connectable to the patient's skin, and a retaining element releasably coupleable to the fastening element to lock the position of the catheter on the fastening element.