Eighty-seven patients who underwent a late secretory phase endometrial biopsy while taking clomiphene citrate (CC) for ovulation induction were studied. Of the endometrial biopsies, 21 (24%) showed an endometrium greater than 2 days out of phase (OOP) with respect to the subsequent menstrual cycle. All 87 patients were categorized by age, weight, CC dosage, and underlying disease entity. The patients then were evaluated by these categories in relation to the incidence of an OOP biopsy while taking CC. Patients with a diagnosis of hypothalamic amenorrhea were statistically more likely to have an OOP endometrium. No other subgroup showed an increased or decreased incidence of OOP biopsies. Conception and spontaneous abortion rates were similar among patients with in-phase biopsies and those with out-of-phase biopsies, which subsequently were corrected with further medical therapy. An aggressive approach to the diagnosis and treatment of luteal phase insufficiency in patients who receive CC for ovulation induction is recommended.