The right subclavian artery was inadvertently punctured during attempted preoperative insertion of a right subclavian venous catheter in a 59-yr-old woman undergoing radical hysterectomy. Large supraclavicular swelling became apparent soon after the arterial puncture. The postoperative chest X-ray obtained approximately 24 h after the catheterization revealed significant elevation of the right hemidiaphragm, which was further augmented on the 2nd to 4th postoperative days; oxygenation was concurrently impaired during these days. It was clinically judged that the hemidiaphragmatic paralysis was responsible for the elevated diaphragm. Both chest roentogenogram and arterial blood gas analyses started to improve on the 5th day, finally returning to normal on the 6th day. It is unlikely that the surgical procedure caused the paralysis, because it dealt only with the lower abdomen. Rather, the attempts at the subclavian venous catheterization probably caused the phrenic nerve paralysis, because the phrenic nerve travels very close to the subclavian vessels. Both the large haematoma formation following the arterial puncture and the time course of the paralysis suggest that compression of the right phrenic nerve by the haematoma, rather than needle trauma, was responsible for the paralysis.