BackgroundAlthough concha bullosa (CB) is the most common variants of the middle turbinate, mucocele of CB is uncommon. Furthermore, CB mucocele with orbital invasion and secondary frontal sinusitis has not been reported previously.Case presentationA 42-year-old Korean male presented with gradually progressive proptosis of right eye and right-sided frontal headache. He had previously undergone endoscopic sinus surgery (ESS) 15 and 9 years ago. The endoscopic examination showed an expansive, large middle turbinate with normal mucosa filled the majority of right nasal cavity and displaced the septum to the left. A computed tomography and magnetic resonance imaging showed a well demarcated cystic huge mass at right nasal cavity extending to ethmoid sinus and orbit. The mass caused a bony defect on the lamina papyracea and displaced medial rectus muscle and orbit laterally. Moreover, the right frontal and ethmoid sinus was totally opacified. This article reports orbital invasion and frontal sinusitis complicating a CB mucocele, which was successfully treated by endoscopic resection of the lateral wall of CB and frontal sinusotomy.ConclusionsThis case illustrates that CB mucocele could develop to such a massive extent that it leads to orbital complication and secondary frontal sinusitis. Therefore, we consider this entity in the differential diagnosis of orbital complications and secondary sinusitis caused by intranasal mass.