The conversion of EEG findings and the evolution of clinical signs was investigated in 7 CJD patients who underwent serial EEG recordings along the course. At the onset of PSWC (mean 8.7 weeks), 5 patients had already progressed to akinetic mutism (characterized by loss of verbal contact and directed responses); and a CJD-typical-movement disorder (myoclonia, exaggerated startle reaction or focal dyskinesia) had started in 5 patients. When akinetic mutism commenced (on average at 7.5 weeks), runs of frontal intermittent non-peaked rhythmical delta activity (FIRDA) were found in all cases. These were later replaced by PSWC in 6 patients (interval 1 to 3 weeks). Occurrence of PSWC was often negatively related to external stimuli (2 of 6 cases), and sedative medication (all patients tested). We conclude that the selection of EEG recording dates to detect PSWC in CJD-candidates should be guided by detailed information about movement disorders and conscious level. Regarding the short survival time after their onset (average 8 weeks), PSWC usually mark the terminal stage of CJD. To detect PSWC, especially, EEG registrations in advanced stages are often necessary. In earlier disease stages, FIRDA-like EEG activities should be regarded as compatible with this diagnosis, and encourage further EEG studies for the demonstration of PSWC in a more advanced stage of CJD.