Eighty-six children with cerebral palsy (CP) born as a product of twin pregnancies were studied. Data regarding their co-twins were also gathered. The authors' findings suggest that (1) monozygotic twins have a higher risk of CP than dizygotic twins, (2) twin order at birth does not seem to be a relevant factor in the etiology of CP, (3) mothers less than 24 or more than 34 years of age had the highest incidence of children with CP as a product of a twin pregnancy, and (4) the data do not support a genetic basis for the disease.