This series of cases of infantile spasms comprised 107 children born between 1960 and 1976 in the county of Uusimaa, Finland. The incidence of the syndrome was 0.38 to 0.42/1000 live births and has remained almost unchanged during those years, although there have been changes in the size of different aetiological groups. The importance of prenatal and perinatal factors, and especially of neonatal hypoglycaemia, as causal factors has decreased, whereas the numbers of cases due to infections and malformations has increased. Compared with investigations in other countries, this Finnish series differs in the incidence of familial cases and congenital cytomegalovirus infection, and especially in the higher incidence of neonatal hypoglycaemia and the lower incidence of tuberous sclerosis.