An apparatus and a method for treating adipose tissue lo-cated beneath apatient's skin is disclosed herein. In some embodiments,the apparatus includes a sonotrode 140 and an ultrasound transducer 130operative to induce longitudinal and/or transversal ultrasound vibrations ina least a portion of the sonotrode 140. In some embodiments, the apparatusprovides a "cold" or "transverse" mode where ultrasound energy deliveredto the patient is primarily energy of transverse ultrasound waves, and a"hot" or "longitudinal" mode where ultrasound energy delivered to the pa-tientis primarily energy of longitudinal ultrasound waves. The longitudinalwaves may be useful for 'pre-heating' tissue of the patient before deliveringthe transverse waves.
