The widespread use of ovulation-inducing drugs to enhance fertility has raised concerns about its potential effects on breast cancer risk, as ovarian stimulation is associated with increases in estrogen and progesterone levels. We investigated the short-term relation between fertility drug use and mammographic breast density, a strong marker of breast cancer risk, among participants in the Group Health Breast Cancer Screening Program. Data linkage with Group Health automated pharmacy records identified 104 premenopausal women < 50 years old who obtained a mammogram during 1996--2006, within 2 years after a fertility drug dispensing. Premenopausal nonusers of fertility drugs were matched to users by age, body mass index, age at first birth, family history of breast cancer, past use of birth control hormones, race, and education (n = 1005). All mammograms were categorized for density according to the Breast Imaging Reporting Data System as entirely fat, scattered fibroglandular, heterogeneously dense, or extremely dense. Density in fertility drug users was equally likely as in nonusers to be rated entirely fat [odds ratio (OR), 0.83; 95% confidence interval (95% CI), 0.18-3.71], heterogeneously dense (OR, 1.09; 95% CI, 0.64-1.85), or extremely dense (OR, 0.93; 95% CI, 0.48-1.78) compared with scattered fibroglandular. In analyses restricted to fertility drug users, each additional month after the date of dispensing was associated with a 13% (95% CI for the OR, 1.01-1.27) increased odds of being categorized as heterogeneously/extremely dense compared with entirely fat/scattered fibroglandular (P = 0.04). Our results indicate no overall association between fertility drug use and mammographic density, but provide evidence that density may be lower in women more recently dispensed a fertility drug.