We report a case in which routine chest roentgenograms of an 840 g infant led to the belief that the peripherally inserted central catheter (PICC) was appropriately positioned within the superior vena cava when, in actuality, it was within the azygous arch. Although many cases of pleural effusions have been reported to be caused by a central venous catheter, a right-sided hydrothorax caused by azygous vein rupture from the use of a PICC is an extremely rare complication. Sudden changes in the condition of a preterm infant with PICC should raise the suspicion of a catheter-related problem.