Young women aged 13-18 who were surveyed in a 1986 study of child welfare clients were over 50 percent more likely to have had sexual intercourse than those in a comparison group drawn from a national sample of young women; they were also more than twice as likely to ever have been pregnant. The child welfare teenagers also scored significantly lower than their counterparts on a test of sexuality and birth control knowledge. Among the child welfare clients (half of whom were at home and half of whom were in foster care), the young women living in foster homes were less likely than those living with their own families to have ever had sex voluntarily (33 percent vs. 47 percent). However, the foster children were less likely to have used birth control at their most recent intercourse or to have obtained contraceptives from a family planning clinic. Nearly half of the foster care teenagers and 40 percent of the teenagers living at home reported having been sexually abused. Victims of sexual abuse were especially likely to be sexually active. Among blacks, the teenagers in foster care and their national counterparts were similar in the proportions who had had sexual intercourse, who had had voluntary intercourse and who had ever been pregnant. Among whites, however, the foster care teenagers were about four times as likely as their matched peers to have had intercourse and to have had voluntary sex, and they were almost eight times as likely to have been pregnant.(ABSTRACT TRUNCATED AT 250 WORDS)