National estimates of demographic characteristics are shown for infertile women compared with those who were fecund, women with primary versus secondary infertility, and infertile women who had, and had not, sought infertility services. Overall, 30% of infertile women had primary infertility, and 70% had secondary infertility. Women with primary infertility were twice as likely to seek services as women with secondary infertility. Many demographic characteristics of women with secondary infertility who sought services differed from those of women who had not sought services. There were fewer differences among women with primary infertility. These findings have implications for the generalizability of results from clinic-based studies and suggest that more research is needed on the barriers to service among infertile couples.