• Mothers and fathers rated the personality of twin children, using the Childhood Personality Scale (CPS). Fathers characterized children as less attentive, zestful, and talkative than mothers. Boys were rated as more attentive, hyperactive, ebullient, and sociable; girls were described as more placid and talkative. Monozygotic (MZ) twinships were much more similar than dizygotic (DZ) on the attention, behavior modulation, and sociability dimensions. Monozygotic and DZ twins both had a high degree of intrapair similarity in zestfulness and verbal expressiveness. Monozygotic twins whose parents thought they were DZ or were not certain of zygosity were as alike as MZ twins believed to be MZ. All three MZ groups were different from DZ twins. Thus, parental expectation did not appear to strongly influence similarity in attention, behavior modulation, and sociability. This suggests the strong genetic contribution to their emergence.