Objective: To assess young women's breast health knowledge and explore its relation to the use of screening mammography. Methods: A convenience sample of 180 women aged 25-45 residing in Toronto, Canada, with no history of breast cancer and mammography received an information brochure and four questionnaires which assessed their knowledge of breast health, sociodemographic/clinical characteristics, and intended decision to use screening mammography. Results: Women's overall baseline knowledge score ranged from 0-18 with a mean of 10 and SD of 3.9. About half of the participants had a low score (0-9), 31 per cent did not know that the risk of breast cancer increases with age, 43 per cent did not know what was the appropriate age to start breast self examination (BSE), and 48 per cent did not know how frequently BSE should be performed. The overall knowledge score was significantly higher for those women who intended to use screening than those who did not (10.8 vs. 8.4, p less than 0.001). The intended use of screening was associated with women's knowledge (p less than 0.001), self-perceived health (p = 0.02), perceived susceptibility to breast cancer (p = 0.04) and perceived usefulness of information (p = 0.001). Conclusion: The study demonstrates that breast health knowledge is limited even among highly educated young women. This finding suggests the need for providing breast health education to women at earlier stage in their life when they have ample time to go through a logical series of decision stages on their way to adopting a new behaviour. (Contains 4 tables.)