Transurethral microwave thermotherapy is being applied as a minimally invasive treatment for alleviating the symptoms of urinary outlet obstruction associated with benign prostatic hyperplasia. Treatment progress has traditionally been guided in its effective power by rectally and urethrally measured temperatures, whereas intraprostatic temperatures would be preferred for feedback purposes. A critical evaluation is presented of intraprostatic thermometry techniques that have been suggested, the techniques currently being used and investigated, and the problems that remain to be solved. Techniques for noninvasive temperature measurement and detecting tissue response during thermal therapy are discussed in more detail. Results presented in the literature have shown magnetic resonance imaging and ultrasonic imaging to be adequate thermometry modalities. For treatment monitoring of transurethral microwave thermotherapy, ultrasonic imaging is especially promising. Future research will indicate whether the promise evolves into a sound clinical technique.