A total of 59 children from multiple pregnancy, aged from 18 months to 13 years, have all shown a mental development within or above normal limits.In 18 children there are reasons to suspect the presence of a CNS lesion, although the general mental level is good.The numerical concordance of intelligence quotients is not typical for MZ and DZ twins. In four cases there were marked qualitative differences despite IQ concordance.The behavior of twins in their home, preschool, and school environment, is determined by the separate nature of the relationship in which the twins live since birth.