通过对254例智力低下(MR)患儿的染色体检查发现典型的21三体综合征32例,进行了临床和细胞遗传学分析。高龄孕妇是引起21三体综合征的重要因素,但不是唯一的因素。父母酗酒,从事有害工种、孕母服药保胎等约占46.87％,提示我们为了减少本综合征的发生,加强环境保护和妇女孕期保健的综合措施是十分必要的。 A clinical and cytogenetic analysis of 32 typical trisomy 21 cases was performed by chromosomal examination in 254 children with mental retardation (MR). Pregnant women is an important cause of trisomy 21 syndrome, but not the only factor. About 46.87% of them were parents of alcohol abuse, engaged in harmful occupational diseases and pregnant women taking drugs, suggesting that in order to reduce the incidence of this syndrome, comprehensive measures to strengthen environmental protection and women’s health during pregnancy are very necessary.