There are many problems in scanning pleural lesions that need to be understood by the referring clinician. First and foremost, the lesion must be pleural based to avoid interposed aerated lung. Second, if the two criteria of pleural fluid are met (changing shape with respiration and floating strands), the likelihood of a successful thoracocentesis is high, but if only an echo-free space is found, the lesion may be fluid, but the possibility exists that it could be a solid mass, pleural thickening, atelectasis, or consolidation. Third, small volumes may be impossible to locate. And fourth, interaction between the clinician and sonographer is essential. If a thoracocentesis is unsuccessful on the ward and ultrasonic guidance is desired, subsequent attempts should be done in the ultrasound laboratory.