The relationship between length of prediagnostic history and course and sequelae of childhood bacterial meningitis was prospectively examined by collecting data from 286 children with bacteriologically confirmed bacterial meningitis. The cases were divided into three groups: short (< or = 24 hours, N = 141); intermediate (> 24 to 48 hours, N = 75); and long (> 48 hours, N = 70) history. The level of consciousness and serum C-reactive protein normalized sooner during hospitalization in patients with a longer history. They also showed neck stiffness more often and longer and had thrombocytosis earlier and more prominently than patients with a shorter history. The differences were not influenced by etiology, sex or age. The occurrence of neurologic abnormalities in the hospital or during the first 6 months after discharge was not affected by duration of illness before hospitalization. We conclude that our results support the view that bacterial meningitis presents in two forms. At presentation the more acute form often has a history of less than 24 hours and poses a great danger to the patient. In contrast the other form develops insidiously and is more difficult to detect but does not have a worse prognosis than the acute form.