This paper deals with a long term follow-up study on psychological symptoms in four patients with microscopically microcephaly induced by prenatal exposed to atomic bomb. They were exposed to atomic bomb at 8- and 12-week-embryos. The distance from the center of the explosion was 780 - 1180 m. All their mothers had acute radiation hazards. Their growths in the uterus were markedly damaged. Postnatal body weight ranged between 1,300 and 2,000 g. They were commonly characterized by microcephaly, physiological and mental retardation, stigmata of degeneracy, and skin symptoms, who were diagnosed as ''microcephaly induced by early prenatal exposure to atomic bomb'' by the research group for microcephaly in the Ministry of Health and Welfare. These common symptoms such as microcephaly, stigmata of degeneracy, and disturbed growth, but neurological symptoms such as motor aphasia were slighter in these patients than in those having congenital Minamata disease prenatal. These results suggested that the prognosis of these patients in whom 30 years have passed is unexpectedly serious.