Plastic bronchitis (PB) is a rare disease, characterized by the formation of obstructive branching airways tracheobronchial casts. Commonly, PB often complicates the course of cardiac or respiratory disorders. The occurrence of PB before manifestation of the underlying respiratory disease is unusual. We report on the case of a boy, aged three years and eight months, free from underlying pulmonary disease, who presented with extensive atelectasis of the left lung during an acute respiratory tract infection. Bronchoscopy revealed the obstruction of the left tracheobronchial tree with large purulent casts. After bronchoscopic removal of the casts, the boy became asymptomatic. Initial aetiological investigations were negative. Two years later, the patient developed an asthma.