To establish clinical markers for canine necrotising meningoencephalitis ( nme ) and to elucidate its pathogenesis, glial fibrillary acidic protein ( gfap ) and anti‐ gfap autoantibodies were measured in the cerebrospinal fluid ( csf ) of 32 dogs with nme , 23 dogs with other inflammatory central nervous system ( cns ) diseases, 27 dogs with miscellaneous cns diseases and 25 healthy dogs, including five pugs. The dogs with nme had the highest levels of anti‐ gfap autoantibodies. The diagnostic sensitivity and specificity of anti‐ gfap autoantibodies for nme were 91 per cent and 73 per cent, respectively. Some of the dogs with nme and the healthy pugs, had high csf concentrations of gfap , suggesting a breed‐specific fragility of astrocytes. The leakage of gfap and the development of autoimmunity may be key to understanding the pathogenesis of nme .