Two brothers had infantile epilepsia partialis continua alternately involving both sides of the body. The children rapidly developed severe psychomotor regression and cerebral atrophy. A brain biopsy specimen showed evidence of chronic inflammatory changes. Extensive investigation did not provide evidence of a specific viral pathogenesis, mitochondrial disorder, or any identifiable neurodegenerative genetically determined disorder. This illness has the features of Rasmussen chronic encephalitis, in which bilateral involvement is quite unusual. Although few patients with bilateral hemispheral involvement have been described, to our knowledge there have been no reported cases involving affected siblings. The familial disorder described herein may represent yet another variant of the classically sporadic and unilateral childhood form. This group of disorders is probably immunologically determined