OBJECTIVE Although studies of serum anti-Müllerian hormone (AMH) in predicting ovarian reserve are numerous, many studies utilized patients under age 40. However, the assessment of ovarian reserve is especially critical in older infertile women. This study evaluates the significance of AMH level in patients over age 40 at the time of their first in vitro fertilization (IVF) treatment. METHODS Forty-nine women over age 40 were studied. Although serum samples were taken prior to their IVF treatments, the data of serum AMH of patients were not taken into consideration to determine the therapy strategy, including follicle induction in which clomiphene citrate and human menopausal gonadotropin were used. RESULTS Twelve out of 49 patients achieved a clinical pregnancy (24.4 %). There was a positive correlation between serum AMH levels and the number of oocytes retrieved (P < 0.0001). The ROC curve analysis for prediction of poor ovarian response, ≤3 retrieved oocytes, showed that the optimum cut-off level was < 1.0 ng/mL for AMH. The lower AMH group (AMH < 1.0 ng/ml) showed less chance of undergoing embryo transfer than the higher AMH group (AMH ≥1.0 ng/ml). There was no difference in pregnancy rate between the two groups. Five out of 12 pregnant women exhibited AMH levels of less than 0.4 ng/ml. CONCLUSIONS Assessment of serum AMH concentration in older patients is useful for the prediction of oocytes numbers which may be obtained in IVF. A cut-off level of 1.0 ng/ml AMH can be used to predict poor ovarian response. This cut-off level of AMH of 1.0 ng/ml might be useful to predict whether patients could have an embryo transfer, but had no power to predict achieving pregnancy. On the other hand, our data also showed that patients over age 40 with extreme low levels of AMH still had a chance of pregnancy.