Some investigations of IUD use have demonstrated impaired ability to become pregnant after removal, while others have not. None of these studies, however, have adequately considered such potentially influencing variables as age and a history of pelvic inflammatory disease (PID). To study the effect of length of IUD use, IUD type and the modifying influences of age and PID history on time required to conceive, we followed women trying to become pregnant after removal of their IUD. Five hundred forty women in Ljubljana, Yugoslavia who were first fitted with an IUD between 1964 and 1972 and had their IUD removed in order to become pregnant were followed through 1980. We found no relationship between the duration of IUD use or type of IUD used, but increasing age and a history of PID each decreased the monthly probability of conception. These findings, along with other recent work, indicate that IUDs are a safe and efficacious contraceptive for women at low risk for sexually transmitted diseases. :Previous investigations of IUD use have demonstrated impaired ability to become pregnant after removal, while other studies have not. None of these studies, however, have adequately considered such potentially influencing variables as age and a history of pelvic inflammatory disease (PID). This investigation uses regression analysis to assess the influence of various factors individually on time to conceive. 540 women in Ljubljana, Yugoslavia, who were 1st fitted with an IUD between 1964 and 1972 and had their IUD removed to become pregnant, were followed through 1980. The COX regression model is used to assess simultaneously the influences of length of IUD use, device type (Lippes Loop), age at removal, parity, previous PID history, and duration of marriage on time to conception, thus controlling for the interrelationships between variables. This technique estimates the probability of conceiving at different times. Results indicate that duration of IUD use did not affect the time to conception. In addition, IUD type, duration of marriage or parity did not affect the time required to conceive. These findings demonstrate that the use of IUDs does not, in and of itself, lead to problems with subsequent fertility. However, these results underscore the importance of limiting IUDs to women who are not at high risk of sexually transmitted diseases.