A woman, aged 59 years, underwent a cortical biopsy that led to the diagnosis of Creutzfeldt-Jakob disease (CJD). A man, aged 46 years, underwent cranial surgery in the same department 3 days later for brain contusion, with an uneventful recovery. Twenty six months later, he developed clinical signs of CJD with a typical EEG pattern. Both cases exhibited features of the 'ataxic' form of the disease with depletion of cerebellar granule cells, without kuru plaques or PrP deposits. PrP deposits were immuno-histochemically observed in the cerebrum, spinal cord and peripheral nerve. Molecular genetic analysis performed on brain tissue revealed the codon 129 polymorphism to be Met129Met in the donor and Met129Val in the recipient. The shared 'cerebellar' phenotype and the genotypic discrepancy between the two patients lead us to postulate that the 'cerebellar' agent strain plays a major role in CJD phenotype and transmission.