OBJECT: The object of this study was to determine if etiology and age at surgery were linked with fevers and altered white blood cell and CSF laboratory values after cerebral hemispherectomy. METHODS: Seizure etiologies (n = 76) were classified into hemimegalencephaly (HME), cortical dysplasia (CD), infarcts (stroke), Rasmussen encephalitis (RE), history of infections, and Sturge-Weber syndrome (SWS) and were compared with clinical variables, maximum daily temperature (Tmax), and blood and CSF studies through Day 12 posthemispherectomy. RESULTS: The Tmax on Days 2-4 and 9-12 postsurgery were higher for HME and RE cases than for stroke cases. Patients with RE showed positive correlations, whereas those with SWS had negative correlations between Tmax and age at surgery. Blood WBC counts on postsurgery Days 3, 6, and 9-12 were higher in the HME and CD cases than in the stroke and RE cases. The percentage of blood polymorphonuclear cells (%bloodPMNs) was higher in the RE cases than in the HME, CD, and SWS cases. The RE, HME, and CD cases showed positive correlations between %bloodPMNs and age at surgery. The percentage of blood monocytes (%bloodMono) was higher in the patients with HME than in those with stroke or RE. The HME and CD cases showed negative correlations between %bloodMono and age at surgery. The CSF red blood cell counts were higher in the RE than in the CD and stroke cases. The percentage of CSF monocytes was higher in patients with CD than in those with stroke and RE. The percentage of CSF lymphocytes positively correlated with age at surgery. CONCLUSIONS: Seizure etiology and age at surgery were associated with developing fevers and altered blood and CSF values after pediatric cerebral hemispherectomy. These findings indicate that besides infections, other clinical variables have an impact on developing fevers and abnormal laboratory values posthemispherectomy. Cultures appear to be the most reliable predictor of infections.