The aim of this study was to identify the common features in a study group of patients with spontaneous cerebrospinal fluid (CSF) rhinorrhoea, to develop a hypothesis to explain the cause of this condition and to investigate the outcome of surgical techniques adopted to repair the leak. In this retrospective study the authors have reviewed all the cases of spontaneous CSF leaks attending and receiving treatment from the otolaryngology department of Queen Elizabeth Hospital, Birmingham, from 1992 to 2002. Of 34 patients with CSF leaks, 15 were spontaneous in nature and formed the study group. Of these 15 patients, 14 were female; with ages ranging from 37 to 70 years and a median age of 50 years. All the female patients were overweight with a body mass index (BMI) >24.9 and, of these, nine were considered obese with a BMI >30. It was attempted to identify common factors in the study group and it was evident that female sex, obesity and age played a key role in this condition. The follow-up period ranged from two to 98 months. Thirteen patients were asymptomatic but two patients remained symptomatic, one of these despite repeated surgical intervention.