The survey of 1,077 consecutive skull fractures admitted to the Massachusetts General Hospital between July 1, 1969 and July 1, 1979 were reviewed. One hundred sixty-eight basilar skull fractures (15.6%) were diagnosed according to clinical and radiological criteria. In 128 patients with basilar skull fracture but without CSF leak, two out of 65 patients (3.1%) who received prophylactic antibiotics developed meningitis in contrast to none of 63 patients who were treated. Nine of 15 patients with otorrhea developed meningitis regardless of treatment. Of 18 patients with rhinorrhea, 13 were treated with prophylactic antibiotics and were free of meningitis but 2 of 5 patients not treated (40%) did develop meningitis. The overall incidence of CSF leak was 20.8%. There is no clear evidence to demonstrate that prophylactic antibiotics are effective in general in reducing the incidence of meningitis after basilar skull fracture with active rhinorrhea. However, the difference in the incidence of meningitis between the treated and the untreated group was noteworthy though not statistically significant. Meningitis can develop despite antibiotic prophylaxis. Additional investigation and therapy should be considered whenever the clinical situation warrants.