OBJECTIVE To determinate the true incidence of treatment-independent pregnancy in an in vitro fertilization programme. To establish and to compare the characteristics of couples with and without spontaneous pregnancy. To analyze the outcome of pregnancies. TYPE OF STUDY Retrospective. SETTING In Vitro Fertilization Unit, Conception's Hospital, Marseille, France. SUBJECTS 594 couples having attempted one or more IVF procedures. The study concerned low-fertility couples (484) ruling our true sterile couples (110). RESULTS Spontaneous pregnancies occurred in 54 couples (11.2%). The characteristics of the two populations were not statistically different, except a shorter duration of infertility (p < 0.05) in spontaneous pregnancies. The rate of ectopic pregnancies in the spontaneous pregnancies was statistically higher than that observed in IVP pregnancies (12% versus 6.5%). The fertility rare of these couples was very low (0.38%). CONCLUSION Spontaneous pregnancies in vitro fertilization programmes are not rare. The evaluation of the results of the in vitro fertilization requires taking the possible spontaneous pregnancies into account.