When fractures of the frontal sinus involve the posterior table or outflow tract, late complications such as mucoceles or mucopyoceles may occur. Surgical removal of the lesions rarely produces cerebrospinal fluid (CSF) leakage. Authors present a case of 34- year-posttraumatic frontoethmoid mucocele combined with CSF leakage. During the marsupialization of the mucocele, unexpected CSF leak was encountered and repaired endoscopically. After discharge, the patient was again administered due to severe headache and found to have tension pneumocephalus which was improved by conservative treatment. It is imperative to take into account the potential for CSF leakage when treating mucoceles or mucopyocles even decades after trauma.