In 1981, as in 1980, most abortions in the United States were obtained by young women, unmarried women and white women, and were performed in the first eight weeks following the last menstrual period (approximately six weeks after conception). The proportion of abortions obtained by unmarried women has increased slightly, and the fraction obtained by teenagers has decreased, mainly because of shifts in the distribution of these groups in the population. The percentage of abortions that are repeat procedures has increased, representing more than one-third of all abortions. The increase is due largely to the rise in the number of women who have had a first abortion, and who are, therefore, exposed to the risk of having a second procedure. Eighty-five percent of all abortions are performed by vacuum aspiration. Dilatation and evacuation is the method used in two-thirds of abortions performed more than 12 weeks past the last menstrual period, and in nine out of 10 abortions that are performed between the 13th and the 15th week. About three percent of women aged 15-44 obtained abortions in 1981, and 26 percent of pregnancies were terminated by abortion--the same fractions as in 1980. About six percent of 18-19-year-olds had abortions--the highest rate of any age-group. The abortion rate (the number of abortions per 1,000 women aged 15-44) and ratio (the number of abortions per 100 live births and abortions) are much higher for unmarried than for married women.(ABSTRACT TRUNCATED AT 250 WORDS)