To determine the effect of intravaginal micronized P on pregnancy rates in clomiphene citrate and letrozole ovulation induction cycles in women with polycystic ovary syndrome (PCOS).Retrospective chart review.University-based assisted reproductive technology program.Women with PCOS who underwent ovulation induction with either clomiphene citrate (n = 90) or letrozole (n = 31) from January 2002 to December 2008.Clomiphene citrate (50–250 mg × 5 days) or letrozole (5 mg × 5 days) were used for ovulation induction. After either intercourse or IUI, patients received intravaginal micronized P (200 mg twice daily) according to prescribing physician preference.Clinical pregnancy rate.In clomiphene cycles, clinical pregnancies were documented in 15.3% of cycles (19 of 124) in the P group, compared with 12.1% (11 of 91) of the non-P group. In letrozole cycles, clinical pregnancies were documented in 21.1% of cycles (8 of 38) in the P group, compared with none (0 of 13) in the non-P group.Women with PCOS who used letrozole for ovulation induction had higher clinical pregnancy rates when using intravaginal P support. Luteal supplementation with P should be strongly considered in women with PCOS, especially in those using letrozole for ovulation induction.