In the evaluation of 39 patients with untreated and treated luteal phase defect (LPD), serial ultrasonographic monitoring of follicular development identified three morphologically distinct growth patterns: normal-sized follicles, small follicles, and luteinized-unruptured follicles. All three patterns were observed in both untreated (46% had normal-sized follicles, 39% had small follicles, 15% had luteinized-unruptured follicles) and treated patients. A small follicle was observed uncommonly in histologically corrected LPD patients (6%). However, a luteinized-unruptured follicle (38%) may persist or be induced in situations where clomiphene citrate has been used to correct LPD or induce ovulation. Ultrasonographic evaluations of follicular growth in luteal phase defect support the theory that luteal phase defect represents a spectrum of normal and abnormal ovarian cycle events.