There is disclosed a drainage system (1) for body fluids comprising a catheter (2) having a distal segment (2a) adapted to be inserted within the body of a patient and a proximal segment (2b) arranged in use outside the body of the patient, a plurality of openings (4) for the passage of the fluids from the outside of the catheter (2) to the inside of the catheter (2), a spacing device (3) of the catheter (2) from the tissues of the patient, which comprises an expandable balloon (8) arranged helixwise about the distal segment (2a) laterally with respect to the openings (4). The catheter (2) defines, on the relative external surface, a groove (5) adapted to at least partially accommodate the expandable balloon (8). There is also disclosed a fastening device (10) for a drainage system (1) comprising a fastening element (11) forming a through-seat (14) for inserting the catheter (2) and connectable to the skin (7) of the patient, and a retaining element (12) releasably coupleable to the fastening element (11) to lock the position of the catheter (2) on the fastening element (11).
