To the best of our knowledge this is the first prospective study in nonhuman primates of proven fertility in the wild, which compares fertility between animals with spontaneous minimal endometriosis and those with a normal pelvis. During 7 months 13 female baboons were exposed to males and all pregnancies were terminated by hysterotomy. A diagnostic laparoscopy was performed to assess the presence of pelvic endometriosis at the end of the fertility trial. Sixty-one percent of the baboons became pregnant at least once and the cycle fecundity was 21%. No obvious difference was found between baboons with (n = 7) and without endometriosis (n = 6) in either pregnancy rate (57 and 67%, respectively) or cycle fecundity (18 and 24%, respectively). These data suggest that in baboons with spontaneous minimal endometriosis the cycle fecundity is not grossly reduced.