To determine the nature and possible reasons for the increasing trend in plural births in the United States during the 1980s. We performed a descriptive analysis of births in the United States for five racial and ethnic groups from 1980–1989, using the United States vital records natality files. The rates of twin and triplet births rose 19 and 100%, respectively, during the 1980s. Approximately onefourth of the observed increases can be attributed to rising maternal age. The increases in twin and triplet births occurred mainly among more educated and older white women. The association of high education status with rising rates of plural births, independent of maternal age, suggests that the observed increase is the result of increasing use of fertility-stimulating therapy among a subset of the childbearing population.