Recent reports implicating elevated cytokines in the central nervous system in a small number of patients studied with autism have reported clinical regression. These studies have not focused on tumor necrosis factor-alpha as a possible marker for inflammatory damage. A series of 10 children with autism had clinical evaluation of their serum and spinal fluid for inflammatory changes and possible metabolic disease as part of their neurological evaluation. Elevation of cerebrospinal fluid levels of tumor necrosis factor-alpha was significantly higher (mean = 104.10 pg/mL) than concurrent serum levels (mean = 2.78 pg/mL) in all of the patients studied. The ratio of the cerebrospinal fluid levels to serum levels averaged 53.7:1. This ratio is significantly higher than the elevations reported for other pathological states for which cerebrospinal fluid and serum tumor necrosis factor-alpha levels have been simultaneously measured. This observation may offer a unique insight into central nervous system inflammatory mechanisms that may contribute to the onset of autism and may serve as a potential clinical marker. More controlled study of this potentially important observation may prove valuable.