This article estimates the number of US women of reproductive age who need infertility services because they want to have children but suffer impairments of their or their partners' fecundity; it also estimates the number who have obtained such services. Analysis is based on data from the 1982 National Survey of Family Growth (NSFG), which involved a nationally representative sample of 7969 women aged 15-44 of all marital statuses. An estimated 3.5 million US women have fecundity impairments that could possibly be treated. 69% of these women say they would like to have children (or more children) and are therefore defined as needing infertility services. For 1/2 the couples in need, it is the woman who is thought to have the fecundity impairment; in only 10% of couples is the male partner described as having the problem. 49% of couples in need have received medical attention. The unmet need (51%) is concentrated among younger women: 72% of those who have not obtained services are under age 30. Blacks and Hispanics each constitute about 15% of the unmet-need group, as do nonmetropolitan women. 22% are poor and 6% are Medicaid recipients.