We report a patient who developed a large subcutaneous hematoma during internal jugular vein catheterization. We usually find the internal jugular vein by advancing the needle along the medial border of the lateral head of the sternocleidomastoid muscle. The external jugular vein should be identified to avoid puncture. But the external jugular vein is known to exhibit variations in its formation and course. During internal jugular catheterization especially for advanced venous access, identifying the external jugular vein by sono probe may be important.