Abstract: Device for hyperthermia treatment in a body cavity comprising a catheter (10) to be introduced into the body cavity and being closed at the distal end thereof. An elastically expandable hose piece (18) is mounted at this end, which is sealingly connected to the catheter at both ends of the hose piece. Two passages (11, 12) extend through the catheter and can be connected each to an associated liquid conduit (26, 27) at the proximal end of the catheter. The passages open under the hose piece through side apertures (21, 22) in the catheter so that the hose piece can be expanded as a balloon by the supply of liquid through one passage liquid being drained off through the other passage. The device comprises external means (28, 31) for circulating liquid through the hose piece on the catheter and heating of the circulating liquid.