This study aimed to determine the frequency and outcome of possible cerebral herniation in relation to lumbar puncture (LP) in postneonatal infants and children with pyogenic meningitis in the tropics. Children with meningitis aged between 6 weeks and 15 years (mean age 4.07 years; n=123) were recruited consecutively over 3 ½ years at the University of Maiduguri Teaching Hospital, Nigeria. The frequency of possible herniation was determined by clinical evaluation in relation to the severity of illness (high versus low risk) on presentation and performance of LP. Previously described scoring schemes were used. Eighteen (15%) patients had evidence of herniation on presentation. The relative risk (RR) of herniation in high- versus low-risk patients was 66.6 (9.3 to 477.1, 95% CI), p<0.0001 while the RR of death or neurological sequelae in high- versus low-risk patients was 2.6 (1.8 to 3.7, 95% CI), p<0.0001. In 99 patients with known outcomes who had LP on presentation, 21 of 81 without herniation pre- or post-LP, four of four with herniation pre- and post-LP, seven of eight with herniation post-LP only, and five of six with herniation pre-LP only died or recovered with sequelae (χ2 = 25.24, df = 3, p<0.0001). It is concluded that outcome depends on the severity of illness and the presence and timing of herniation. A policy of selective rather routine LPs may improve the outcome in meningitis in developing countries.