Plastic bronchitis is a rare disorder characterized by formation of large, branching bronchial casts, which are often expectorated. We present an interesting case of a 35-year-old woman who presented for evaluation of a chronic cough productive of voluminous secretions. Clinical and radiological examination confirmed a total left lung atelectasis without any pathological mediastinal node. Flexible bronchoscopy demonstrated tenacious, thick, and sticky whitish secretions blocking the left stem bronchus. This material was extracted, and inspection demonstrated a bronchial cast, whose pathological analysis revealed necrotic epithelial cells, some eosinophils, and Charcot-Leyden crystals. Two days after bronchoscopy, the patient rejected more bronchial casts, and dyspnea improved. Control of chest x-ray revealed complete left lung aeration and the diagnosis of idiopathic plastic bronchitis was obtained. This article shows the interest in clinical practice to evoke the diagnosis of plastic bronchitis in front of a productive chronic cough. Our case illustrates a rare clinical presentation represented by an atelectasis of an entire lung.