We performed a retrospective study of infantile spasms (IS) in 57 children (19 girls and 38 boys) from the east-central region of Sweden for the period 1987-1991. The incidence was 0.45/1,000 newborns a year, with a spread of 0.17-0.76 between the seven counties included. Forty-three cases (75%) were symptomatic and 14 (25%) were idiopathic. Cerebral malformations were diagnosed in 8 children, and chromosomal aberrations were diagnosed in 5. In addition, 2 children each were diagnosed as having tuberous sclerosis and neurofibromatosis. At follow-up, 57% in the idiopathic group had normal development, whereas 91% in the symptomatic group had died or developed a multihandicap. The value of modern neuroradiological techniques for etiological diagnosis is stressed.