Abstract: An A-mode ultrasound echography method is employed for monitoring the position of a patient during hyperthermia treatment. A therapy apparatus includes a therapy device having at least one ultrasound therapy transducer and at least one monitoring ultrasound transducer, where the ultrasound monitoring transducer is linked to an electronic circuit for processing A-mode signals and is part of an A-mode echography device. The therapy apparatus further includes a device for causing the ultrasound transducer operating in A-mode to transmit a brief signal and to receive the echo of the brief signal. A comparing device compares the echo received with a reference echo, and transmits the result of the comparison to a control device.