Prospective evaluation of 155 couples with two or more consecutive pregnancy losses disclosed uterine morphologic abnormalities in 27%, chromosomal abnormalities in 21 individuals (7.7%, or 15.4% of the couples), and at least one abnormal diagnostic test suggestive of a cause for recurrent pregnancy losses in 106 (68%). A positive test for antinuclear antibody was found in 7.5% of the women, whereas the expected rate in a population of this age is less than 2%. Cervical cultures for Ureaplasma urealyticum (T-strain mycoplasma) were positive in 48% of the women, and 28% of these women had a genetic or uterine abnormality to explain their pregnancy losses. Thyroid function profiles and cervical cultures for Mycoplasma hominis provided no significant information in the evaluation in these couples. With the exception of women with a positive antinuclear antibody, the overall prognosis for later pregnancies was quite good whether the diagnostic evaluation of the couple was normal (77% subsequent live births) or abnormal (71% subsequent live births). The significance of the positive antinuclear antibody in these women is unclear, but further studies and long-term evaluation are necessary to determine the relationship between recurrent pregnancy losses and later development of collagen-vascular diseases.