Background Coinciding with the relatively good and improving prognosis for patients with stage I–III breast cancer, late recurrences, new primary tumours and late side-effects of treatment may occur. We gained insight into prognosis for long-term breast cancer survivors. Patients and methods Data on all 205 827 females aged 15–89 diagnosed with stage I–III breast cancer during 1989–2008 were derived from the Netherlands Cancer Registry. Conditional 5-year relative survival was calculated for every subsequent year from diagnosis up to 15 years. Results For stage I, conditional 5-year relative survival remained ∼95% up to 15 years after diagnosis (a stable 5-year excess mortality rate of 5%). For stage II, excess mortality remained 10% for those aged 15–44 or 45–59 and 15% for those aged 60–74. For stage III, excess mortality decreased from 35% at diagnosis to 10% at 15 years for those aged 15–44 or 45–59, and from ∼40% to 30% for those aged ≥60. Conclusions Patients with stage I or II breast cancer had a (very) good long-term prognosis, albeit exhibiting a small but significant excess mortality at least up to 15 years after diagnosis. Improvements albeit from a lower level were mainly seen for patients who had been diagnosed with stage III disease. Caregivers can use this information to better inform (especially disease-free) cancer survivors about their actual prognosis.