Using Medline File, 295 articles which deals with both multiple births and congenital anomalies were obtained out of total 1,680,029 ones, during 1976. 01-1982. 05. These articles constitute the combinations of form and content. The form consists of three major categories : 1) original case(s) report, 2) population study (incidence study) concerning multiple births with particular anomalies and 3) general remarks. The content was classified into research study regarding the etiology of congenital anomalies and/or multiple births and practical aspects such as prenatal diagnosis, genetic counselling, care or treatment of the patients and monitoring or surveillance. The sets among original case(s) report include 231 twins, 16 triplets and one quintuplet. In 231 twins were seen 141 MZ, 56 DZ and 34 unknown zygosity. As for concordance or discordance, rates of concordance were 68.1% for MZ and 61.1% for DZ, respectively. Rates of discordance were 31.9% for MZ and 38.9% for DZ, respectively. A few incidence studies indicated that the frequencies of congenital anomalies were higher in twins than in singletons, and also higher in the same-sexed twins or MZ than in the opposite-sexed twins or DZ. The etiology of congenital anomalies oftenly seen in twins was considered to be classified into three categories : 1) common cause to MZ twinning as well as congenital anomalies, 2) vascular interchange between each member of MZ twins and 3) intrauterine crowding usually seen in both MZ and DZ. These three categories were in good agreement with the causes in 141 MZ above mentioned.
