The apparatus comprises an ultrasonic vibration generator (1) and a lens (2) affixed thereto adapted to focus the ultrasonic vibration at a predetermined zone. It may be used to destroy certain types of cancerous cell which lie close beneath the surface, such as skin cancers and other melanomas. Other cosmetic skin treatments may also be carried out, such as restructuring collagen molecules in order to tighten and restructure skin tissue, depilation and to destroy dyed tissue and thereby aid removal of unwanted tattoos.