The total population of children under 10 years in one Swedish urban area and one rural area was screened for infantile autism (IA) and autistic-like conditions (AC). A total prevalence of 6.6 per 10 000 was found, which is somewhat higher than in previous similar studies of the same region. Infantile autism accounted for two-thirds of the cases. Boys far outnumbered girls, but this was entirely accounted for by the IA group. The preponderance of autistic boys was less pronounced among the severely mentally retarded children. Mental retardation was seen in almost 90% of cases and only one child had an IQ exceeding 100; clinical and laboratory signs of brain dysfunction were also found in a majority of cases. Distribution by social class was no different in either patient group from the general population.