The authors studied, from the clinical and electroencephalographic points of view, 22 patients with parasagittal convulsive focal activity with a phase reversal at the vertex. The selection of cases was purely electroencephalographic. The authors conclude: 1. Primary focal discharges in the parasagittal region are rare (0,5%) when the EEG is not activated; they are more frequently found in infancy and childhood. 2. The parasagittal focus may lead to bilateral diffuse synchronous discharges (secondary bilateral synchronism) through some subcortical centers (presumably the thalamic reticular formation). Those discharges were present in 6 cases. 3. Those discharges can be similar to the primary bilateral synchronism found in the P.M. epilepsy and can be characterized by three fundamental aspects: a) irregularity of discharges; b) a single phase reversal at the midline; c) asymmetry at the vertex region. 4) From the clinical point of view the adversive (45%) and akinetic seizures (18%) were the most frequently found. 5. Secondary bilateral synchronism can be associated with absence seizures (observed in 2 cases only); these seizures however are very different from these called "centrencephalic" for they are associated with several types of clinical, signs. 6. Epileptogenic lesion in the mesial aspect of cerebral cortex could be responsible for akinetic seizures. The authors found these seizures in 4 patients and in all of them the focal discharge was represented by slow waves (1 to 4 c/sec) of high voltage and with a phase reversal at the vertex.