An oligomenorrheic infertile patient with evidence of vitamin B12 (cobalamin) deficiency is described. Treatment consisted of clomiphene citrate, human chorionic gonadotropin (hCG), conjugated estrogens, dexamethasone, and ferrous sulfate. Pregnancy occurred after 1,000 micrograms of vitamin B12 was added to the treatment regimen. We believe the patient's infertility was in part related to the megaloblastic anemia. A possible correlation between vitamin B12 deficiency and failure to ovulate is presented.