The present study examined whether changes in the incidence of infantile spasms could be used to evaluate changes in the quality of pre- and perinatal care over time. 107 children in 1960 to 1976, and 102 in 1977 to 1991, developed infantile spasms in southern Finland. The number of small-for-gestational age (SGA) infants and infants with neonatal hypoglycaemia decreased significantly. Brain malformations, malformation syndromes and patients with tuberous sclerosis increased; this probably reflects the development of more refined neuroradiological screening methods. SGA infants are probably more apt to develop infantile spasms than preterm infants appropriate for gestational age. Early prenatal factors seem to play a major role in the genesis of infantile spasms. Little can be done to reduce the incidence of infantile spasms, but every effort should be made to reduce the number of SGA infants by good prenatal care. Treatment of hypoglycaemia is important because infantile spasms might be preventable in these infants.