In the paper, a patient suffering from Ewing's sarcoma is presented. She was treated with chemo- and radiotherapy. As one of the methods of monitoring of the course of treatment and follow-up after finishing it has been ultrasound examination. In the ultrasound examination I have observed gradual diminishing of the tumor, up to it's complete disappearance. In the bone there have remained only two small hyper-echogenic focuses not changing their shape or size. At the beginning in Doppler examination a large arterial flow was found in the tumor, having low vessel resistance. In the course of treatment systolic velocity decreased and vessel resistance increased up to complete disappearance of the flow in the visible small hyper-echogenic focuses in the bone.