The combined experience at two institutions was reviewed to evaluate endometrial biopsy and the prognosis for pregnancies affected by endometrial sampling during the cycle of conception. In the evaluation of 1,084 patients, 1,174 biopsies were performed. Twenty-seven endometrial biopsies were done during the cycle of conception, with spontaneous abortion occurring in six cases (22.2%). Multiple diagnoses were made (including luteal phase defects, endometritis and polyps), and interruption of pregnancy occurred. Several cases illustrate disturbing complications. Methods of minimizing pregnancy interruption and patient discomfort are available.