Bacterial meningitis is a medical emergency requiring early diagnosis and therapy in order to reduce mortality and morbidity. Although fever is the most sensitive sign, occuring in a majority of patients, it may be absent, especially in oldest patients. Most patients have alterations in mental status but coma is more frequent in meningitis caused by S. pneumoniae. Focal neurologic signs are present in about 25% of the cases and are again much more frequent in the setting of pneumococcal meningitis. In adults with suspected meningitis, mass effect on CT-scan is unfrequent and as a consequence, the risk of lumbar punction is negligible. Very early administration of antibiotics, even before hospital admission in case of suspected meningococcal infection may result in a decreased abilty to identify the etiologic agent by cultures. The use of new techniques for detection of bacterial antigens and the development of rapid PCR assays may be particularly helpful in patients who had received antibiotics before lumbar puncture.