To evaluate the risks involved in post infertility pregnancy, the perinatal outcomes of 571 patients with infertility treatment in 9 institutions were analyzed by questionnaire retrospectively. The rate of multiple pregnancy and premature delivery was 14.5% (83/571) and 13.3% (76/571) respectively. Multiple pregnancies occurred in 33 cases with ovulation induction, 22 cases with artificial insemination by the husband (AIH) and 25 cases with in-vitro fertilization by embryo transfer (IVF). Premature deliveries occurred in 32 cases with ovulation induction. 26 cases with AIH and 14 cases with IVF. Three babies were dead and 4 babies were handicapped. In single post infertility pregnancy, the rate of premature birth was twice as high (9.0%) as in normal controls. The mortality rate was 0.45% (2/449), which was higher than that of controls. This suggests that post infertility pregnancies tend to result in multiple pregnancy and premature birth. In addition, in single post infertility pregnancies there was the possibility of poor perinatal outcome.