There is evidence that aspirin use reduces the risk of breast cancer. Increased mammographic density is known to be associated with increased breast cancer risk. Little is known about the association between mammographic density and aspirin or other non-steroidal anti-inflammatory drug (NSAID) use, but it is possible that the association between aspirin use and breast cancer risk might be due to the effect of aspirin on mammographic density. Multiple linear regression was used to investigate the association between measures of mammographic density and the use, frequency, and duration of aspirin and other NSAIDs such as paracetamol (acetaminophen), arthritis medication, and other over-the-counter or doctor-prescribed pain medications in 3286 women from the Australian Mammographic Density Twins and Sisters Study and the Genes Behind Endometriosis Study. We found no association between either dense area or percent dense area with any of the NSAIDs examined (all P > 0.06). If aspirin is reducing the breast cancer risk in women, it is likely doing so via a different pathway other than mammographic density measures that predict breast cancer risk.