We investigated whether poor adherence with metformin tablets may have contributed to the poor success rates seen in the metformin-containing arms of the Pregnancy in Polycystic Ovary Syndrome (PPCOS) Trial. Median adherence for both metformin and clomiphene citrate tablets was within acceptable limits and unrelated to ovulation: thus, failure to comply with physician recommendations for metformin dosing was not the reason for low ovulation and pregnancy rates in the PPCOS Trial.