Effects of long-term administration of anticonvulsant drugs on chromosomes in epileptic mothers and their children were examined. Specimens from peripheral lymphocytes were prepared by incubation for 3 days and colchicine treatment. Results obtained were as follows: (1) The incidence of abnormal cells in the epileptic mother group over 9 years of drug administration was significantly higher than in the group below 9 years. (2) Most of chromosome abnormalities found in subjects were of comparatively simple morphological aberrations such as gaps or breaks. The incidence of the chromosome-type abnormalities was significantly higher in the patient group than in the control group. (3) Chromosome abnormality of children showed a positive correlation with that of mothers but was not significant. (4) The incidence of chromosome abnormality in children was reduced along with aging. (5) These observations could be interpreted to suggest that chromosome abnormality appearing in children born from epileptic mothers under drug therapy was probably formed by direct effects of anticonvulsant drugs on the fetal hematopoietic system.