Though clear indications for its clinical application are not established yet, balloon sinuplasty technology per se is considered safe and very few severe complications have been mentioned in literature as of today. We report the case of a 36-year-old female patient who presented with right sided rhinorrhea from a CSF-leak in the ethmoidal roof after balloon sinuplasty, aimed at her right frontal sinus. Apparently, the surgeon was unaware of having penetrated the skull base through the lateral lamella of the cribriform plate intraoperatively. CSF rhinorrhea became evident 3 weeks postoperatively only when fever, headaches and moderate nausea developed. Upon revision, diameter, size and shape of the bony defect exactly matched with the tip of a standard sinus balloon catheter device, as could be demonstrated and documented. A small posttraumatic encephalocele had intermittently blocked the leak. Endoscopic surgery and duraplasty were performed under intrathecal fluorescein control, applying CT image-guided navigation. Since two-layer fascia lata closure of the defect, the patient has remained free of symptoms without any evidence of CSF leakage. Balloon sinuplasty per se is considered a safe technique, though in inexperienced hands or wrongly applied, complications may occur, as with any surgical tool rigid enough to breach through skull base.