We describe a hyperinflation of the paranasal sinus system with fatal outcome in a macaw. The bird was presented with signs of acute respiratory distress. Initial examination revealed a voluminous bullous mass that occluded the pharyngeal cavity and obstructed the glottis. Postmortem examinations, including diagnostic imaging, gross pathology, histopathology, microbiology and molecular biology led to the diagnosis of a sinus pneumocele of the mandibular part and paratracheal recessus of the left infraorbital sinus. The bird suffered from chronic sinusitis, rhinitis and arteriosclerosis. History and histopathological findings provided indications of a nutritional imbalance and poor animal husbandry as a possible primary cause. The formation of mucoceles adjacent to the pneumocele supports the idea that occlusive chronic inflammatory alterations of the opening into the blind-ending sinus compartments resulted in a unidirectional inflow of air. Subsequent inflation into the pharyngeal cavity caused fatal upper airway obstruction.