A central nervous system infection due to Morganella morganii is uncommon. We report a case diagnosed at the neurological department of Fann teaching hospital in Dakar, Senegal. A 12-year-old boy was hospitalized for acute meningoencephalitis. The CT scan was normal and the study of cerebrospinal fluid (CSF) revealed cytological and biochemical abnormalities and M. morganii. HIV and syphilitic serologies were negative and blood CD4 lymphocyte count showed 354 per mm(3). The treatment with cefotaxime associated with gentamicin for 6 weeks was successful. The outcome of infection depends on many factors such as the onset and quality of treatment, the virulence of the germ and the status of immune system.