A child, who had undergone ventriculoperitoneal shunting, presented with repeated episodes of pneumonia and expectoration of CSF. Chest x-ray demonstrated the presence of the shunt catheter in the base of the left lung. In the present case the distal end of the catheter perfored the diaphragm, entering the thoracic cavity through the pleura and penetrating the pulmonary parenchyma. CSF then flowed freely into the alveoli and bronchi and became expectorated during repeated bousts of coughing associated with pneumonia. This respiratory complication disappeared after the removal of the catheter. We theorize that the penetration of the catheter into the thoracic cavity was secundary to its displacement from the iliac fossa to the left infradiaphragmatic space between the spleen and the diaphragm where the intra-abdominal pressure is lowest. The respiratory movements and the hypertension inside the abdomen created a constant friction of the catheter against the diaphragm which was finally perforated, permitting the passage of the peritoneal end of the shunting device into the thoracic cavity and secundary penetration of the lung.