Unilateral lung whiteout is not a common pediatric chest radiograph finding, but when it is encountered, timely and accurate interpretations of the radiograph are required because life-threatening respiratory failure can be associated. Lung whiteout may result from several conditions, and the differential diagnosis has a broad range. We describe 4 pediatric patients with different etiologies of unilateral lung whiteout: a large pleural effusion, mainstem bronchial plugging with a large cast, a mediastinal tumor, and consolidation. The ultimate causal diagnosis may not be initially obvious, but valuable clues can usually be found in the conventional chest radiograph to assist with appropriate early management. Chest ultrasound provides additional information, and we recommend it as the second examination for such patients.