A case is presented in which a guidewire, during subclavian catheterization in a 63 years old patient, became knotted outside the vein, behind the clavear head of the sternocleidomastoid muscle. The wire was easily removed by surgical approach and the post operative course was uneventful. The causes of this complication are discussed and a few main points are emphasized when the Seldinger technique is employed for subclavian vein catheterization.