A retrospective analysis of patients evaluated and treated for infertility was performed. Luteal phase inadequacy was diagnosed when the late luteal endometrial biopsy pattern was greater than 2 days out of phase in two cycles; in patients treated with clomiphene citrate therapy was changed if one biopsy was out of phase. One hundred ninety-seven patients underwent 242 biopsies. Among 137 women no treated with clomiphene citrate, 24 (17.5%) had out-of-phase biopsy specimens; 7 of 24 (29.2%) repeat biopsies were out of phase, with luteal phase inadequacy in 7 of 137 (5.1%) women. The probability of an out-of-phase biopsy occurring by chance alone was 4.2 of 137 or 3.1%. No woman was diagnosed to have luteal phase inadequacy as the single infertility factor. Fifty-three pregnancies (41%) occurred in 130 women without luteal phase inadequacy and in 2 of 7 (28.6%) diagnosed to have luteal phase inadequacy with other infertility factors. In clomiphene citrate-treated patients, pregnancy occurred in 15 of 26 (57.7%) with corrected luteal phase inadequacy and in 21 of 34 (61.8%) without luteal phase inadequacy. In this population the diagnosis of luteal phase inadequacy was not made more frequently than by chance alone. Moreover, fecundity in patients with treated luteal phase inadequacy is comparable to that in patients without this diagnosis.