To determine the diagnostic accuracy of Kernig's sign, Brudzinski's sign, and nuchal rigidity for meningitis, 297 adults with suspected meningitis were prospectively evaluated for the presence of these meningeal signs before lumbar puncture was done. Kernig's sign (sensitivity, 5%; likelihood ratio for a positive test result [LR(+)], 0.97), Brudzinski's sign (sensitivity, 5%; LR(+), 0.97), and nuchal rigidity (sensitivity, 30%; LR(+), 0.94) did not accurately discriminate between patients with meningitis (>/=6 white blood cells [WBCs]/mL of cerebrospinal fluid [CSF]) and patients without meningitis. The diagnostic accuracy of these signs was not significantly better in the subsets of patients with moderate meningeal inflammation (>/=100 WBCs/mL of CSF) or microbiological evidence of CSF infection. Only for 4 patients with severe meningeal inflammation (>/=1000 WBCs/mL of CSF) did nuchal rigidity show diagnostic value (sensitivity, 100%; negative predictive value, 100%). In the broad spectrum of adults with suspected meningitis, 3 classic meningeal signs did not have diagnostic value; better bedside diagnostic signs are needed.