Reexpansion of a pulmonary atelectasis is often difficult, even after removing possible causes of bronchial obstruction. Chest ultrasounds, inexpensive and readily available at the patient bedside, may offer valuable support to guide recruitment maneuvers. We report the case of a 57-year-old woman that developed a complete collapse of the left lung seven days after undergoing an intestinal resection for perforation. A mucous plug occluding the main bronchus was removed with bronchoscopy, but persistent hypoxemia required mechanical ventilation; 24 hours later, an attempt to wean the patient from the ventilator failed. Chest X-rays revealed the persistence of a partial collapse of the left inferior lobe associated with a pleural effusion. A chest ultrasound confirmed the presence of a lung consolidation and of a modest pleural effusion. Manual reexpansion was then attempted, and ventilatory pressures as well as the duration of forced inspirations were based on real-time ultrasound images. Complete reexpansion was achieved within a few minutes and confirmed by chest X-ray. The patient was weaned from mechanical ventilation on the same day and discharged from ICU three days later.