Insect stings and subsequent reactions are common occurrences, but life-threatening systemic reactions are rare. Herein, we describe the case of a young man who developed diffuse pulmonary haemorrhage following an insect sting. He had experienced urticarial reactions to insect stings previously. Diffuse pulmonary haemorrhage should be recognized as an uncommon manifestation of severe systemic reaction to insect sting.