Comparison of 1988 data from the National Survey of Family Growth with 1982 data reveals that the proportion of U.S. women who have had sexual intercourse rose slightly, from 86 percent to 89 percent. Among teenagers, the proportion sexually active rose from 47 percent to 53 percent; most of the change is attributable to increases occurring among white and nonpoor teenagers, thus narrowing racial and income differences. Among women aged 15-44 in 1988 who have ever had intercourse, 67 percent reported that they had had two or more sexual partners in their lifetime. The proportion was highest among women aged 20-34 (about 70 percent), but 58 percent of sexually active teenage women reported having had two or more sexual partners. About 67 percent of women of reproductive age in 1988 were exposed to the risk of unintended pregnancy, up from 63 percent in 1982. Among these women, 35 percent rely on contraceptive sterilization to prevent pregnancy and 55 percent use reversible methods, while 10 percent use no method. Poor women are much more likely than nonpoor women to be using no method of contraception (15 vs. eight percent); among poor teenagers, this proportion reaches 25 percent. The level of contraceptive use at first intercourse among teenage women improved substantially between 1982 and 1988, however, rising from 48 percent to 65 percent. During 1984-1988, almost four in 10 births and almost six in 10 pregnancies among American women were unintended; most of these were mistimed, but 12 percent of births were unwanted ever.(ABSTRACT TRUNCATED AT 250 WORDS)