Acute pulmonary processes present a diagnostic challenge for intensivists and radiologist alike. Only when clinical data and radiographic findings are correlated can patient care be optimized. Although many acute pulmonary process are not unique to the ICU patient, these entities often have atypical presentations in the critically ill patient. Physicians caring for ICU patients must understand the role of the chest radiograph in diagnosing and following such processes as atelectasis, pneumonia, aspiration, or pulmonary embolism.