OBJECTIVE: To determine the reasons for the steady increase in breast cancer mortality in Russia and Ukraine. METHODS: Age-period-cohort analysis, supplemented by analysis of historical fertility trends. RESULTS: Mortality from breast cancer has risen steadily in both countries over the past 40 years, although faster in Russia than in Ukraine. There are strong birth cohort effects, which are consistent with known changes in fertility. Death rates were highest among those born in the first half of the 20th century, declining among those born after the 1950s. There has been a decline in mortality among younger women since the mid 1990s, which may reflect improvements in treatment. CONCLUSION: The increase in breast cancer mortality in Russia and Ukraine can largely be explained by known changes in fertility, while recent changes may reflect changes in treatment. Observed trends suggest that death rates from female breast cancer in the two countries are likely to stabilize or even decline in the future.