Serratia marcescens is an unusual cause of community-acquired meningitis in adults. We report a case of S. marcescens meningitis occurring 29 years after a head injury and preceded by 3 years of intermittent nasal discharge of cerebrospinal fluid (CSF). One month before admission, the patient had received treatment with cefadroxil. This case illustrates the risk of Gram-negative bacillary meningitis in patients with a CSF leak when they are treated with antibiotics. When patients have a chronic clear nasal discharge, one should look for a past medical history of head injury before prescribing antibiotics. In the presence of a fistula, any antibiotherapy may lead to the selection of resistant organisms which may be difficult to treat. Due to the high risk of meningitis and the fact that spontaneous closure in delayed CSF rhinorrhoea is unlikely, surgical repair of any associated fistulae is mandatory.