Long-term effects in a neurosurgically separated twin pair were illuminated by standard psychological test scores obtained over a period from 2 to 38 years of age. Interdigitation of the gyri of their right frontal lobes had necessitated separation in two stages at 4 months of age. One twin clearly suffered some brain injury and showed some impairment during the testing at 5 years of age. The scores of both twins rose at the adult testing. The brighter twin has an IQ comparable to that of the mother. The unique data set is a kind of model for long-term assessment of early brain surgery, particularly with craniopagus twins.