Chest roentgenology in the intensive care unit is a real challenge for the general radiologist. Beyond the basic disease, the critically ill is at risk for developing specific cardiopulmonary disorders, all presenting as chest opacities, their diagnosis often being impossible if based only on the radiological aspect. To make things harder, their appearance can vary with the subject's position and the mechanical ventilation. Patients require a continuous monitoring of the vital functions and their mechanical and pharmacological support, for which they are connected to different instruments. The radiologist should know the normal position of these devices, and promptly recognize when they are misplaced or when complications from their insertion occurred. Our aim is to suggest for each of the above-mentioned conditions a guideline of interpretation based not only on the radiological aspect and distribution of the lesions, but also on the physiopathological and clinical grounds.