Diagnosis, choice of therapy, and pregnancy outcome were analyzed in 79 women evaluated for luteal phase inadequacy. Criteria for the diagnosis were established, and groups at risk for luteal inadequacy were identified. Treatment choices, tailored to the suspected cause, included progesterone suppositories in 54 women, with 23 pregnancies and 19 deliveries; clomiphene citrate in 6 women, with 2 pregnancies and deliveries; and combined treatment in 7 women, with 5 pregnancies and 4 deliveries. Eight women received no treatment, including three who underwent endometrial biopsy in the cycle of conception and who subsequently delivered. These data suggest that careful diagnosis and the proper choice of treatment are important, and that progesterone supplementation may result in improved pregnancy outcome for patients with infertility and pregnancy wastage who have luteal phase inadequacy.