Object. The authors aim to identify the characteristics of primary spontaneous CSF rhinorrhea and propose a hypothesis for its pathogenesis. Methods. Between 2003 and 2009, 21 patients diagnosed with primary spontaneous CSF rhinorrhea underwent surgery in the authors' hospital. The clinical aspects were retrospectively reviewed, and their characteristics were analyzed. Results. There were 18 women and 3 men, whose ages ranged from 37 to 74 years (mean 53 years). Body mass index (BMI) ranged from 22 to 58.8 kg/m(2) (mean 31.2 kg/m(2)). Eighteen patients (85.7%) were overweight, and 18 (85.7%) suffered from headache or tinnitus before rhinorrhea. Radiological images revealed fully or partially empty sellae in 14 patients (66.7%). The preoperative intracranial pressure (ICP) ranged from 11 to 28 cm H2O (mean 17.6 cm H2O), while the postoperative ICP ranged from 21 to 32 cm H2O (mean 25.5 cm H2O, p < 0.01). An endoscope-assisted transnasal approach was chosen for the repair. Postoperatively, in 95.2% of patients a cure was achieved. Rhinorrhea recurred in only I patient, and a leakage from a new defect occurred in another patient 4 years after the operation. Both patients underwent additional surgery, which was successful. The follow-up period varied from 5 to 75 months with a mean of 34 months. Conclusions. All patients had direct or indirect evidence of elevated ICP, most patients presented with symptoms of idiopathic intracranial hypertension (IIH), and most patients were women and obese. Primary spontaneous CSF rhinorrhea may be clue to IIH, and it is a rare symptom of IIH. When treating or monitoring these patients during follow-up. ICP should be controlled, and other symptoms of IIH should be noted. (DOI: 10.3171/2011.3.JNS101447)