OBJECTIVE: Vaginal progesterone suppositories are an accepted treatment for infertility attributed to luteal phase defects. Although oral micronized progesterone may be preferable to suppositories for many patients, there are no studies on its use for patients with luteal phase defects. This study evaluated the efficacy of oral micronized progesterone for the treatment of luteal phase defects. STUDY DESIGN: Seven women with luteal phase defects previously corrected by vaginal suppositories were administered oral micronized progesterone (200 mg by mouth three times a day). Endometrial biopsies were performed to evaluate treatment efficacy. Questionnaires were used to assess side effects, including sedation. RESULTS: On oral micronized progesterone, all patients had in-phase endometrial biopsies. Despite complaints of drowsiness, the majority of patients preferred the oral formulation over the vaginal route of administration. CONCLUSION: We conclude that oral micronized progesterone is efficacious in the treatment of luteal phase defects.