A 50 year old woman developed progressive encephalomyelitis with rigidity over a three year period. Her CSF contained oligoclonal bands and both her serum and CSF contained antibodies directed against GABA-ergic synapses (antiglutamic acid decarboxylase [corrected] antibodies). These antibodies have recently been described in cases of stiff man syndrome. Both disorders may be part of a clinical spectrum that has an underlying autoimmune basis.