Syncope is defined as transient loss of consciousness as a result of cerebral hypoperfusion. Electroencephalography during syncope shows either a 'slow-flat-slow' or a 'slow' pattern. The first is believed to denote more severe hypoperfusion. Although the diagnosis of vasovagal syncope relies primarily on history taking, there is limited evidence regarding the relative importance of various clinical features, and none that relate them to the severity of electroencephalographic changes. The aim of this investigation was to study symptoms, signs and electroencephalographic changes with a 1 s resolution using electroencephalography and video data in 69 cases of tilt-induced vasovagal syncope. The main finding was that flattening of the electroencephalograph indicated more profound circulatory changes: the 'slow-flat-slow' group had a lower minimum blood pressure, longer maximum RR-interval, contained more cases with asystole and had a longer duration of loss of consciousness than the 'slow' group. Second, we describe a range of signs, including some that have rarely been reported in syncope, e.g. oral automatisms. Third, signs occurred at different rates depending on electroencephalographic flattening, suggesting a classification of syncopal signs. Type A signs (e.g. loss of consciousness, eye opening and general stiffening) develop during the first slow phase, stay present during flattening and stop in the second slow phase. Type B (particularly myoclonic jerks) occur when the electroencephalograph is slow but not flat: their abolition with electroencephalographic flattening suggests dependence on cortical activity. Type C signs (making sounds, roving eye movements and stertorous breathing) occur only in the flat phase, whereas type D (dropping the jaw and snoring) may occur either in slow or flat phases. In conclusion, our findings provide a detailed assessment of clinical symptoms in relation to electroencephalographic (EEG) changes during tilt-induced syncope.