The present study examined whether changes in the incidence of West syndrome (WS) could be used to evaluate changes in the quality of prenatal care over time. The incidence of WS in Finland did not change (1960-1991) in spite of increased survival of low-birth-weight infants. Small-for-gestational age (SGA) infants were more apt to develop infantile spasms than preterm average-for-gestational age infants. The number of SGA infants with neonatal hypoglycemia and infantile spasms decreased significantly. The number of cases of brain malformation and tuberous sclerosis increased; this probably reflects the development of more refined neuroradiological screening methods. Early prenatal factors seem to play a major role in the genesis of infantile spasms. Little can be done to reduce the incidence of WS, but every effort should be made to reduce the number of SGA infants by good prenatal care and treating neonatal hypoglycemia carefully.