Within the last 15 years in vitro fertilization (IVF) has become an established treatment modality. Its results compare favorably with that of spontaneous conception in the natural menstrual cycle in fertile women. The possibility of a success for any couple undergoing treatment will, however, depend on their characteristics. Over the past several years, the importance of these individual factors has been subjected to an extensive research. Our group has performed a number of studies that relate the cumulative conception rate (CCR) and cumulative live birth rate (CLR) with the age of the patient, the cause of infertility, and the type of ovarian stimulation used. We have also analyzed the effect of previously successful in vitro fertilization treatment upon the results of a subsequent treatment course, and the obstetric outcome of in vitro fertilization pregnancies when compared to those that are naturally conceived. In this review article, the importance of the above mentioned factors will be discussed in view of our research results and other recently available evidence.