Luteal phase deficiency (LPD), as diagnosed by endometrial biopsy, is not a single disorder but rather a spectrum of dysfunction that reflects both endometrial cycle and ovarian cycle abnormalities. Forty-three patients were diagnosed as having LPD by two consecutive abnormal cycles. Seven patients (16%) with hyperprolactinemia received bromocriptine, and one hypothyroid patient received thyroid replacement. The remaining patients were treated sequentially with progesterone suppositories, clomiphene, the combination, and follicle-stimulating hormone and luteinizing hormone. If no conception occurred in 6 months on a given type of therapy, treatment was advanced. Patients were rebiopsied on each medication. In all, 33 of 41 (81%) compliant patients conceived. No viable pregnancies occurred without normal endometrial maturation, regardless of the treatment modality employed. When compared with time-life table projections, pregnancies occurred at rates comparable to those of a normal population once normal endometrial maturation was obtained with therapy. The endometrial biopsy accurately reflects the functional state of both the ovarian cycle and the endometrial cycle and can be used to determine adequacy of therapy, thereby improving conception rates in patients with LPD and eliminating the need for therapeutic trials.