Sixty-six psychotic children aged between two and 20 years, examined by the same child psychiatrist and diagnosed according to strict criteria as suffering from infantile autism, other psychoses and Asperger's syndrome, were examined with chromosomal cultures in folic-acid deficient medium. 47 per cent of the children showed major or minor chromosomal aberrations. The infantile autistic group comprised a total population of autistic children. The fra(X)(q27) marker was seen in 25 per cent of autistic boys. A subgroup of children with the fra(X)(q27) abnormality, infantile autism, psychomotor epilepsy and brainstem dysfunction was identified. Other chromosome markers and abnormalities occurring in several cases included long Y chromosomes, fra(X)(p22), fra(16)(q23) and fra(6)(q26). The results are discussed and correlated with certain clinical characteristics.