Abstract: Apparatus for delivering in vivo hyperthermia treatments to a subject and methods of performing such treatments are provided. The apparatus comprises an imaging device, such as an MRI scanner, a microwave applicator, and a controller to target particular tissues within the subjects body for hyperthermia treatment. The microwave applicator emits microwave energy toward the target tissue and the imaging device provides real-time feedback as to the position of the applicator relative to the target tissues and thermometry data so as to permit real-time adjustment of the applicators operating parameters.