The purpose of the study was to identify the clinical symptomatology of children with focal sharp waves of genetic nature. Genetic determination was assumed if the EEG of at least one sib revealed typical focal sharp waves. Forty-one probands (27 boys, 14 girls) and their 44 sibs showed a broad spectrum of different seizure types of focal origin including so-called atypical benign partial epilepsy (pseudo-Lennox-syndrome) and febrile convulsions. Numerous cases showed psychomental retardation or selective deficits of development. The classical syndrome of rolandic seizures with normal psychomental development and normal neurological findings was present in only a few cases. Similarly, EEG findings were quite variable. Rolandic sharp wave foci alone were found in only 22% of the probands. The remainder had foci in other regions (17%), or multiple foci (61%). Depending on age at first seizure, 42%-79% of the seizure-affected probands and 50% of the affected sibs showed generalized heritable EEG traits such as 4-7/s rhythms, generalized irregular spikes and waves, and/or photoparoxysmal response. Three pairs of monozygotic twins were concordant for the special type of EEG findings, two of them also for clinical symptoms.